What We Found When X-Raying Some MLB Baseballs | Hacker News Reader

What We Found When X-Raying Some MLB Baseballs

fivethirtyeight.com

245 pointsgscott78 comments

A cool article, laid out to be readily understandable for everyone.

Missing from the discussion, though, is a description of the change in the moment of inertia. If the ball's mass distribution has shifted radially, the moment of inertia can change significantly.

Spin matters very much to the aerodynamics of baseballs. A change in the moment of inertia could have a substantial impact (positive or negative) on the flight characteristics as the ball reaches the batter, the mechanics of the ball/bat interaction (particularly as relates to the spin of the ball leaving the bat), and the outbound trajectory. A lower-moment ball will spin faster initially, but slow its rotation rate more quickly, making any prediction of the overall effect of a change in moment of inertia difficult indeed.

It's funny, because based off the header image on that page [0], that's what I expected the discussion to be about. The center of gravity in those four samples is hugely off.

[0]: https://espnfivethirtyeight.files.wordpress.com/2018/03/juic...

If you scroll down further in the article, you'll see that those are cropped images of the cores. The cropping is off-center, not the cores. Otherwise, they would wobble terribly when thrown or hit.

No, I understand that. But look closely at the x-ray/CT and you'll notice that the rubber is nowhere near even around the core.

The background images appear to actually be a video or something, but here's a screenshot I took:

https://share.neosmart.net/View/Index/nfgSDo.png

The two balls in the first column (so one old and one new) have a pretty symmetric distribution, but look closely at the others. Some are ridiculously uneven.

Yeah, but that doesn't matter here because it's present in both the newer era balls and the older era balls. We also know that seven of these are used baseballs, meaning they could very well be deformed or off center from use. There's a reason that they only use a baseball for about 8 pitches. (https://www.foxsports.com/other/story/major-league-baseballs...)

In cricket the same ball is used for 480 balls (depending of format). Initially the new hard ball is seen as an advantage to the fielding side as a bowler gets more bounce and deviation from the hard seam, but a batsman can also hit it further. There is also the phenomenon of swing (a bit like the curve ball in baseball) which is accentuated by the fielders polishing one side of the ball. As the ball ages and softens it's bounce becomes more true and therefore it favours the batting side. Often towards the end of its life the ball develops 'reverse-swing' where it curves the opposite way. They have to keep the 'rough side' of the ball completely dry to do this, so all fielders have to keep their hands dry. Penalties have been applied to players trying to alter the condition of the ball. Different brands of ball are polished differently and swing at different times. Some even have a lacquer which takes a while to come off and start swinging at all

why I think this is relevant

1) The aerodynamic effects of the kind polish applied dramatically affect performance

2) Since wear on the ball is critical to the long format games, the fans don't get to take one home and sell it on ebay, even if they catch a six (ball hit into the crowd) :(

The significant change in cricket hitting has been massively heavier bats, which used to be made of compressed willow to preserve their life (a whole season for a pro), but are now made of unpressed willow and considered disposable. The unpressed bats work much like corked baseball bats are supposed to, and have transformed the game. Slow-bowlers, like spin bowling where the bowler spins the ball to alter its flight and make it move when bouncing, have to be exceptional now or they get smashed into the car park!

The most significant change in cricket has been covered wickets when it rains. If you have ever had the fun of playing on an uncovered wet wicket you will understand how elite teams were able to be bowled out for under 20 runs on wet wickets.

I also think more body protection has played a massive role in more aggressive batting. When I was young I used to play with nothing more than pads, gloves and a box and had to face bowlers who could bowl over 140km/hr on very unpredictable wickets. I got out more than once getting out of the way of some bouncer that stayed low as I was looking to avoid getting hit. I have been hit enough times with a cricket ball to have learned self-preservation is the better part of valour.

^This.

As a teenager growing up in the UK I played cricket for my school and a local team, and when I was about 14 I had the "pleasure" of facing roughly four balls bowled by the Legendary West Indies cricketer Viv Richards[1] when he visited my school. I somehow managed to get the bat onto the first ball and score a 4, at which I foolishly celebrated shouting something along the lines of "in your face, I thought you were a professional cricketer!" What a stupid, stupid thing to do.

There then followed a three ball lesson in bodyline bowling until I literally lost my bottle and refused to carry on leaving the wicket with what little dignity I had left. Seriously, seeing that giant six-foot tall man taking a run-up and then bowling a cricket ball at my head at what seemed like supersonic speed literally scared the crap out of me.

[1]: https://en.wikipedia.org/wiki/Viv_Richards

You are right about the covered wickets, although when I started watching cricket in the 1990's they were already universal in the elite game. I should correct my statement and say that heavy bats have been the most significant thing in the last 20 years of the elite game with regards to big hitting.

I also agree about protection, being hit by a cricket ball is something you don't forget, and can indeed be lethal[0]

[0]:https://en.wikipedia.org/wiki/Phillip_Hughes

I had no idea that sixes were returned to play[0]. Thanks for that info as well as the rest of your comment :)

0: minus the occasional Chris Gayle blast out of reach of anyone, I imagine

It is possible that a ball can be hit out of a stadium and not be returned (but it is usually very rare due to stadium sizes and layouts).

If that happens they have a tray of prepared balls of different states, then they'll select one that most closely matched the previous one's condition/age etc.

The moment of inertia can change without a change in the center of gravity. Think ring vs. disc. I suspect this is what the GP was talking about.

Moment of inertia changes will also wildly affect a slightly off-center hit, as well as how hard it is to catch the resulting spinning ball.

I really appreciate your spin on this article.

sorry

This single paragraph is all the specifications for a legal ball in baseball[0]:

> 3.01 (1.09) The Ball

> The ball shall be a sphere formed by yarn wound around a small core of cork, rubber or similar material, covered with two strips of white horsehide or cowhide, tightly stitched together. It shall weigh not less than five nor more than 5 ¼ ounces avoirdupois and measure not less than nine nor more than 9 ¼ inches in circumference.

So it leaves a lot of wiggle room, intentional or not, for modifying the baseball to produce different results. As the article points out, 2014 was a great year for pitchers with the fewest home runs since 1995. And that year, 1995, is significant as that was the year of the strike shortened season.

I'm still on the fence as to whether this is a good or bad thing (juiced balls) as in the 20s there were rule changes regarding how balls were treated that led to the live ball era[1] and the greatest baseball legend, Babe Ruth.

Baseball has a way of balancing out over time, so we may see a wild homerun heyday before getting a period of pitching dominance. Both super fun to watch.

0: http://mlb.mlb.com/mlb/official_info/official_rules/official...

1: https://en.wikipedia.org/wiki/Live-ball_era

Naturally since MLB baseballs are basically hand-made. I've seen any number of segments showing how they're manufactured. Very low tech - winding by machine but the covers are sewed on by hand.

Statistics are always a two-edged sword. Using home run statistics to "prove" a ball had changed is folly unless you have the data on balls over many years including the variance which as you pointed out can be significant.

The article says the newer balls differed in mass by 0.5 grams and that this difference was statistically significant

For reference the "not less than five nor more than 5 ¼ ounces avoirdupois" in that rule means 141.747615625 to 148.83499640625 grams. (Yes exactly, the "pound avoirdupois" no longer has any definition except that it's so-and-so many SI kilograms).

So 0.5 grams is a pretty big change, but it's way inside the variation allowed. Given the change in composition it seems to me that such a change is to be expected and actually suggests the ball makers did NOT go out of their way to hide what's happened here.

If MLB did this deliberately without the consent of the teams, some owners might be upset.

As the article points out, players are already adapting their hitting approach to produce more home runs, and presumably that’s at least partially due to the added likelihood of success for that strategy with the juiced balls.

So of course there’s also a team-building aspect of this shift for GM’s to consider. A decade ago, all the smart money was on high “OBP” (on-base percentage) players over boom-or-bust power hitters. If MLB did juice the ball, it shifted the ground out from under tens of millions of dollars of team analytics, and billions in payroll decisions made based on them.

Additionally, trying to do something like this and expecting the infamous stats geeks that follow baseball not to notice seems very short-sighted.

>A decade ago, all the smart money was on high “OBP” (on-base percentage) players over boom-or-bust power hitters.

That is not an entirely accurate characterization, in fact most of the time the moneyball teams valued those boom and bust players more than traditional teams. The actual equation they were using was something close to 3*OBP+Slugging so slugging is good, and they tend to get walks a lot along with their strikeouts so OBP is usually good too.

Yep, "three-true-outcomes" (HR, strikeout, walk) players were seen as undervalued. Much of today's developments can be seen as flowing out of that re-evaluation of the "badness" of strikeouts.

OBP driven by consistent-but-weak contact was the sort of thing that sabermetrics types in 2008ish were shifting away from. Adam Dunn types (high OBP power hitter, low average) were seen as undervalued compared to Juan Pierre types (low power, higher average).

E.g. http://www.firejoemorgan.com/2008/03/this-column-is-eternal....

Fun thing about Pierre vs Dunn - Fangraphs has them practically tied in career WAR in the same number of seasons. But traditional evaluations praised the scrappy Pierre types a lot more than the strikeout-happy Dunn types.

Right. What people always seem to forget about the analytics based approaches, particularly the "moneyball" concept is that the intent was to identify those undervalued players. If the current trend is to prefer players with attribute X, that means that they'll be more expensive than their relative worth, so identify attribute Y which is also important and you can pay them a lot less.

People still refer to moneyball style approaches as if the exact metrics which were used in 2001 are the end all be all, but as soon as people caught on to OBP and such the real moneyballers were by definition off to something else.

While you're kind of right, I downvoted because I don't think that's the most reasonable or fair interpretation of what they're saying.

I think their point is largely true in two or three ways. The first is that prior to the moneyball era, teams treasured power hitters in a way that was much more OBP agnostic.

The second way is that they underappreciated players who don't hit for power but put up strong OBPs, like Scott Hatteberg.

The third is that however much moneyball teams prized home runs, they certain prize them even more now than before.

I think it's perfectly fair to say these distinctions support the notion that moneyball teams didn't value power hitting the same way as the generations that preceded or followed them.

He might be a little biased, but Justin Verlander tweeted some R analysis on exit velo and launch angle 2014 v 2017:

https://twitter.com/JustinVerlander/status/96939000476931686...

Seems the balls are flying farther?

There's an assumption that Major League Baseball cares about fair competition and integrity, but those things are much less important than you might think.

In the 1990s, a very large number of players used performance-enhancing drugs (PEDs). Those who were honest and declined to use them were penalized by being less competitive (a problem any time you allow corruption - the market favors the corrupt and weeds out the honest), undoubtedly some losing their jobs and dreams.

MLB did nothing, other than to change the rules and ban the use of the drugs. The cheaters suffered no penalties and their records stand; the victims, including honest players as well as fans, no compensation or even official acknowledgement (that I know of). One of the most prominent cheaters has a job as a coach on major league teams, including as a hitting instructor for many years. Another had his jersey retired by his team and was inducted into their team Hall of Fame, and now has a job with them. (The cheaters are having a hard time getting into the national Hall of Fame, but that's due to sportswriters and others voting against them, and they are coming closer each year.)

Does MLB care if the balls are juiced, or if current players have discovered new ways to cheat?

This article really does a good job of making this topic accessible to those of us that live outside of the 'land of the free'. The graphics and UX are really neat.

The research does prove that the ball has changed.

However, the composition of the ball has changed many times over the years with new technology and new rules. It should be possible to look back at when the core changed from rubber to cork (for example) and to see the effects this has had. This bigger narrative could be useful in understanding what has gone on lately.

https://en.wikipedia.org/wiki/Baseball_(ball)

Exit velocity and launch angle of the ball have only been recorded since 2014. 2015 league-wide. That's why this latest change is causing all this analysis.

Is anyone else surprised by the sample size? I'm not sure that eight baseballs provides enough data for any relevant conclusions, especially when the differences are so small to begin with.

If all the balls have shown variations within the same tolerances, that would be true, but balls grouped in a meaningful way, and these groups have shown negligible differences among themselves.

Because of this tight variation within the groups, 8 balls are enough IMHO.

Assuming there has always been 50% light balls and 50% heavy balls, the probability of picking 4/4 heavy balls from the earlier period and 4/4 light balls from the later period by chance is 0.4%.

Although this statistic might be less relevant if the balls were not statistically randomly selected.

Presumably the eBay balls were probably homers or hit into the stands, no?

They could also be foul tips or grounders thrown to the crowd.

Something I rarely hear discussed around the MLB home run boom, maybe because it's just too obvious (?):

Warm weather -> less dense air -> balls fly farther. Recent years have been record warm. Does that have any measurable or meaningful effect?

Similar discussion on cricket ball and how science shows no impact of weather on balls flying through air significantly enough but still remains a common misconception through out the sport's fraternity.

http://theconversation.com/why-we-think-the-weather-affects-...

It's certainly been discussed in the forums I've read, and it could certainly account for some of it, but the mid-season spike in home runs starting in 2015 seems to point to at least one additional factor that would be somewhat consistent across all ballparks (including climate controlled). The balls seem to be one of the only factors that would account for that.

Air density does have an effect, but the density change from temps that we've seen in the last few years (say a 75 degree game vs an 80 degree game) is only going to get you a couple feet of ball travel. While it make a difference on balls that just barely clear the fence, it definitely doesn't account for the entire boom in home runs.

For comparison, a ball hit 400 ft at Yankee Stadium (400 ft elevation) would go 440 ft at Coors Field (5280 ft elevation). That's a 10% increase in ball distance for a 17% decrease in density. Increasing the temp by 5 degrees F drops the density by 0.8%, which is probably only good for 1-3 feet.

https://chem.libretexts.org/Exemplars_and_Case_Studies/Exemp...

https://wahiduddin.net/calc/calc_da.htm

Baseball is such a data-driven sport, and numbers don't tend to lie. There's always always some new form of juice, some changes to the mound, something going on with the bats and balls...

* Baseball just saw its biggest home run surge since the steroids era. Here’s why. - The Washington Post || https://www.washingtonpost.com/news/fancy-stats/wp/2016/03/0...

The real graph to pay attention to: https://img.washingtonpost.com/wp-apps/imrs.php?src=https://...

Do the materials in a baseball show up differently over time, say over a 20-30 year span? I'd really want to see this done on more sets of baseballs. In addition to testing players, if the goal was consistency it would be prudent to scan the balls, do a core sample of the pitcher's mound every game, make sure bat composition and temperatures are consistent... The new pitch clock isn't going to empower pitchers either though, look for batter power to rise again next year.

I find the referenced https://fivethirtyeight.com/features/in-mlbs-new-home-run-er... more interesting.

It suggests the lower air resistance makes pitchers throw faster, too.

I would think lower ridges also made pitchers throw more predictable balls. That may have made going for a big hit a more profitable strategy.

Definitely, here is a key sentence: "The decrease in drag is probably a result of a smaller, slicker baseball with lower seams."

The article ignores the fact that it is air resistance on the seams that creates the "break" in a curve ball. Less drag, less effective curves, ergo, advantage to the batter. So more HRs might come from less effective pitching.

The MLB might be well-advised to accept this analysis (together with FiveThirtyEight's previous analysis suggesting that the rest of the uptick might be explained by an increase in batters swinging upwards), as one alternative putative explanation for this uptick would be that there has been a development of new and undetectable methods of doping.

It's just speculation, but I would not be at all surprised if there are protocols designed to maintain HGH and testosterone near the allowed limits.

Combine that with moderate improvements in training and there you go, 35 year olds that can train like they are 20.

While last year didn't see particularly outsized top end homerun figures (like the old steroid days), the increase in the huge number of people hitting 20 and 30 or more homeruns is interesting. That plays to the notion of what you mentioned about staying near limits, as a lot of people saw a lift; alternatively, the ball is juiced. Stanton and Judge hitting 50+ is very odd historically as well.

2010: 18 players hit >= 30 homeruns. 77 players hit >= 20 homeruns.

2011: 24 players hit >= 30 homeruns. 68 players hit >= 20 homeruns.

2012: 27 players hit >= 30 homeruns. 79 players hit >= 20 homeruns.

2013: 14 players hit >= 30 homeruns. 80 players hit >= 20 homeruns.

2014: 11 players hit >= 30 homeruns. 57 players hit >= 20 homeruns.

2015: 20 players hit >= 30 homeruns. 64 players hit >= 20 homeruns.

2016: 38 players hit >= 30 homeruns. 111 players hit >= 20 homeruns.

2017: 41 players hit >= 30 homeruns. 117 players hit >= 20 homeruns.

Something substantial changed in 2016.

Can exit (exit from bat) velocity, trajectory and spin be measured and used with the climate conditions at time of hit to compute an expected batted ball distance which could then be compared to actual batted ball distance, with changes over time identifying possible ball changes?

Has anyone tested different runs of baseballs by hitting them and seeing how far they go?

Something I didn't see covered in the article (maybe I missed it) was a discussion of errors. If the ball is moving faster and potentially with more bounce, wouldn't we also expect to see an uptick in fielding errors?

Possibly, but this would somewhat be countered by the fact that you can’t get a fielding error on a home run.

Edit to add more context: Home runs are much more common than errors - in 2017, there were a total of 2,820 errors, less than half the number of home runs. One of the more common types of fielding errors is dropping a fly ball, so it wouldn’t take a huge percentage of would-be dropped fly balls converted to home runs to counter any uptick in fielding errors due to the ball being bouncier.

This smacks of some kind of inadvertent formulation change (like a company started buying a component from a new supplier that met whatever specs they were measuring, but resulted in a ball with significantly different characteristics). Now that's it's been a couple of years, the MLB is not going to change it back.

Heard a segment on this on Pardon the Interruption on ESPN yesterday. I agree with their argument that it's not a bad thing because we are in a time of sports where games need to be more exciting. We want more home runs, and more scorings, and if lighter baseballs means that we get them, then it's just a normal progression.

in a time of sports where games need to be more exciting

There's a problem with this, though. Home runs are only exciting when they're relatively uncommon. If the home run trend continues, we will effectively see the disappearance of everything else that makes up the game of baseball. Players will either hit a home run, a flyout, or a strikeout. Risky plays (small ball) such as hit-and-runs, sacrifice bunts, and stolen bases will see a continued decline. This will sap all of the strategy and nuance out of the game, turning it into pure spectacle.

Not what I want. Not what a lot of baseball fans want.

>Risky plays (small ball) such as hit-and-runs, sacrifice bunts, and stolen bases will see a continued decline. This will sap all of the strategy and nuance out of the game, turning it into pure spectacle.

I thought it was pretty well established that bunts, stealing, hit and run are all bad strategy. Entertaining but not anywhere near optimal play.

right, which is bad because it results in an extremely dull game. it’s not inherent to the rules of baseball, though. the easier it is to hit for power the more this is true.

imagine if we averaged 0.5 home runs per game instead of the current 1.8. suddenly you’d need a lot more small ball type strategy to have any hope of scoring runs.

If we accept lighter baseballs as a way to get more home runs, what's wrong with corked bats or any other mechanical mechanisms that could be used to juice home runs? Sammy Sosa was suspended 8 games for using a corked bat, which was claimed was supposed to only be for practice and was used accidentally.

https://en.wikipedia.org/wiki/Corked_bat#History_of_use_in_M...

I suppose like any other sport, baseball is picky and arbitrary about what's OK and what's not OK when it comes to changing equipment and standards.

I once read an article about the 'sport' of speedwalking that drove this point home to me. This is a sport, where pretty much the only rule is that one foot must always be touching the ground at all times. But in the age of video, it's pretty clear that this one rule is violated by every speedwalker every race. But the ruling body of the sport didn't care about any of the video evidence, and doubled down on using judges with a set of criterium to determine if walkers had both feet in the air.

My other takeaway was that if your sport can't enforce it's only major rule, because physics, they'll find ways to lie to themselves to maintain the status quo. It's probably a profound lesson in politics if I really think about it.

The difference is that - in theory anyway - all of the balls are the same.

> we are in a time of sports where games need to be more exciting

Not just games, but everything from the US (I live in Europe) seems to need to create spectacles where there are none with as much flashbang as possible. Just look at the difference in BBC documentaries vs ones coming from the US.

This trend kicked into high gear around 2000 and I had to stop watching channels like Discovery as they no longer aired documentaries but entertainment shows.

In the end, I stopped watching TV altogether as a result of this and we haven't had a TV subscription of any kind since around 2005. My wife uses Netflix once or twice a month though when my sister visits.

I imagine someone at Ralings ”refining” the process and then placing bets for the season on number of homers or some other metric that would payoff.

If it is in fact a variation, one should be able to create a subscription service that sends out regular testing results on the balls, along with bets that capitalize on the information asymmetry.

Maybe just a classic case of trying to make more money by saving on material costs and passing it off as the same product?

If all teams use the same baseball, does this matter? Probably not. At least the game feels more exciting with more homers...

Nonetheless, good research...

Stuff like this just makes me weep for sample sizes. All this data, but now another variable to account for in _everything_.

Will climate change have an effect on home runs? I'd imagine there would be more home runs in warmer years.

This is a beautiful and well written article, but I find the argumentation rather weak. Let's roll up the reasoning backwards:

The article claims that changes to three factors (weight, bounciness and air resistance) could have caused a 25 percent increase in the number of home runs[1]. The increase in the number of home runs could be from the possibly altered balls flying farther [2].

The factors they looked into are weight, bounciness and air resistance and their contributions break down as follows:

- 5 feet, less air resistant, according to previous research [3]

- 3 feet, increased speed around 0.6 mph, according to previous analysis of bounciness [4]

- 6 inches, decreased weight by 0.5 g of the ball, which their analysis did not show. [5]

Never mind that 5 feet 6 inches is a little less than 8.6 feet.

When it comes to bring the argument home the article either refers to other sources instead of linking the claims together or it suggests a connection it fails to support. All the lengthy talk about the composition of the core is interesting and I enjoyed reading about it. It could have been used to support the argument about the overall weight, except the article didn't show a significant change in overall weight. It could have been used to support the argument about bounciness, but it fails to draw that conclusion while referring to previous research in a hand-wavy way.

I think they should just have skipped the CT scans, thermogravimetric analysis and the scanning electron microscope analysis. For the saved money they should have bought more balls. They could have weighed them precisely and measured their bounciness. This wouldn't have made such a beautiful article but it would have probably made a much stronger argument.

--------

[1] "According to Nathan’s calculations, this would lead to a more than 25 percent increase in the number of home runs. Asked whether these changes in combination could have significantly affected the home run rate, MLB declined to comment."

[2] "Combine all these factors together — a lighter, more compact baseball with tighter seams and more bounce — and the ball could fly as much as 8.6 feet farther."

[3] "According to a previous analysis performed by The Ringer, that increase in bounciness alone would add around 0.6 mph to the speed of the ball [..]"

[4] "[..] previous research at FiveThirtyEight showed that they also became less air resistant. The decrease in drag is probably a result of a smaller, slicker baseball with lower seams. The change in air resistance could add an additional 5 feet to the travel distance of a fly ball."

[5] "The overall weight of the balls also dropped by an average of about a 0.5 grams between groups, but, unlike with the cores, this difference was not statistically significant.x

The ball as a whole weighs much more than the core alone, and there was more variation in the weight of the full baseballs than in the weight of the cores, both of which meant that the bar for statistically significant variations in weight was higher for the whole baseball than for just the core."

Can you unpack their explanation of [5]? It rings false to me, because I think it's based on a false assumption of the distribution of baseball weights. I think their assumptions are that both the weights of the total ball and weight of the core follow normal distributions, but after showing that the cores do not, they continue to assume that the weight of the whole balls does. This feels like one of the classic critiques of frequentist statistics, where effect size gets conflated with sample size.

Worse, shouldn't we presume that there is a (strong) quality control step, which eliminates the tails of the distribution for overly heavy and overly light balls, but perhaps not for heavy and light cores? Which means that our assumptions that both the cores and balls follow the same normal distribution for ball weight is wrong from the start, and thus the notion of "statistically significant" shouldn't depend on total weight of the ball.

That is to say, I think the evidence is just as strong that the cores are .5 g lighter as that the balls are .5 g lighter, but it's just a quirk of p-value and our (known-to-be-false0 assumptions of normal distribution that make one conclusion "significant" and the other "not significant". They did find that the balls were .5 g lighter, right?

The cores of the new balls weighed, on average, about 0.5 grams less than the cores from the old group. This difference was statistically significant, which means it’s highly unlikely that it was due to sampling error.

I'm doubtful about their use of statistics here, and whether they actually show what is being claimed. They have 4 "old" balls, and 4 "new" balls, and are making claims about the differences between the pools of (let's guess) 100,000 balls from which they were respectively taken. They then go from here to hypothesize that the measured differences in the samples can explain the number of home runs hit per year.

Assume that instead of baseballs they were trying to talk about mortality rates in small American cities, and their procedure was to sample 4 Americans from each of two cities with different mortality rates, and then run tests on them to determine what's causing the different death rates. While not impossible, it would seem surprising if such a small sample would provide firm evidence toward any conclusion. It would be less surprising if by doing multitude of tests one could come up with something that is "statistically significant" about the differences in the samples.

The first things that bothers me about the article is that they don't give the actual measured values, they just say "this difference was statistically significant". I mean, there are only eight numbers, let's see them! Also, they don't clearly say whether there was overlap in the distributions --- that is, where any of the "old" balls lighter than any of the "new" balls. If there was no overlap, I'd assume they would have said so, so their silence makes me presume overlap. By how much? What assumptions are being made about the distributions?

Second, I wonder what other tests they ran. Presumably, if they were X-raying the balls, they expected to see something different about the interiors, but was this the difference they were planning to test? If you run twenty tests (and only report one of them), you'll probably find a statistically significant result even if it's just by chance. So did they preregister this hypothesis? And what else did they test? One of the odd things about concluding a "lighter core" is responsible for more home runs is that I think a similar narrative could explain why a "heavier core" could also be an advantage.

Third, I wonder about the sampling. Are these balls (which were bought off Ebay) really randomly sampled from the game balls used at the each time? If they were bought from the same sellers, might they have have been from the same batch and thus not randomly sampled? If these were actual game balls, were they sampled from "home run balls" rather than all balls? If so, how does sampling from the extremes change the sample distribution? And might the balls have changed while in storage? That is, might the older balls have heavier cores simply because they are older, perhaps because they've been stored somewhere humid and are absorbing water?

Fourth, rather than hypothesizing about how this tiny observed difference might cause a large difference in number of home runs per season, how about some tests? Do the lighter balls actually fly farther? One might take measurements of a full set of balls, set up a batting practice with a real pitcher a real batter, and measure how far they fly. No, one doesn't have to do this for every article, but one also doesn't have to claim "statistical significance" about every hypothesis. Even if the testing doesn't explain the jump in home runs, it would be nice to have something real in the article beyond hypothesis.

Lastly, has anything else changed? A few different pitchers and a few different batters might also cause a large difference in home runs per season. The weather, the stadiums, night vs day games? The "bonus" paid for hitting home runs? They mention in the article that "The remainder could be reasonably chalked up to a philosophical shift among MLB hitters, who are likely swinging upward to maximize the number of balls they hit in the air and are not shy about the increase in strikeouts that may come with that approach." Rather than than accounting for the "remainder", is there any reason to assume that this doesn't fully account for the difference?

TL;DR: The core of the balls are 0.5g lighter, good for 15cm of extra range. The balls are more bouncy, good for 90cm of extra range. And the balls are slicker/smoother/less air resistant, good for 1.5m extra range. The total of ~2.6m extra range could make the difference for the observed record number of home runs.

Does anyone know what they're using to layout articles like these?

I usually hate the parallax & scroll-jacking effects but they're used really well here.

The animated background image is actually a video [0]. There are class names that contain "scrollmagic" so maybe that's it [1].

[0] https://espnfivethirtyeight.files.wordpress.com/2018/01/juic...

[1] http://scrollmagic.io

Yes, looks like that could be it. Thanks!

Scrubbing through the video like that is quite an interesting technique.

This is such an excellent use of parallax scrolling

Ha! my first thought as well. It's generally used in such a gimmicky fashion, it was nice to see how this actually made the article much more useful.

I hereby object to their use of "air resistant." I know what they're trying to say, but a ball does not resist the air. The air resists the ball. Air resistance is a property of the air, in other words, not the ball. So a ball can't be "air resistant" at all, much less more air resistant or less air resistant. In fact, because air is where the friction and resistance comes from, it seems like "air resistance" as possessed by a ball, would be a good thing. "This ball flies farther because it's more air resistant."

isn't the term "air resistant" describing a relationship between the two components, atmosphere and projectile? The ball absolutely exerts drag on the air as the air rushes past it (imagine a stationary ball in a windstorm). all that is required to apply this to the ball as a projectile is a reference frame that takes the ball as the reference point.

I knew I'd get this comment, hehheh. Sure, it takes two (materials) to (do the friction) tango, and the ball actually does resist the air. But the goal is to move the ball, and a ball game in a vacuum would still be a ball game, so I guess I'm trying to think of a better way to say it. Not having any luck, BTW

They probably should have said the balls [may] have a lower drag coefficient.

This seems like intentional trolling. You are nitpicking a word in the article that did not impede communication. You incorrectly describe friction without even a first semester understanding of physics.

Suddenly realized why the disconnect. You're talking physics (high school physics at that), while I'm only talking about English.

We don't say an airplane is air resistant. We say it experiences air resistance. Case closed. You need to relax, I'm not trolling.

Poor baseball - it's tough when you've got a hundred years of tradition to live up to.

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