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Comment by ggambetta | Hacker News Reader

This looks super interesting. Unfortunately, I couldn't follow the explanation beyond the few first paragraphs because of so much baseball terminology and logic, which is completely alien to me :( The intro is confusing enough, but then there are terms that aren't defined, such as "stealing" - are readers supposed to be able to infer what this means just by context?

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So the whole intro is to make the point that a certain type of play (base stealing) doesn't make sense, even for teams that do it well - and it took until 2012 to figure that out and get their players to stop doing that play.

Ceteris paribus, base stealing doesn't make sense. But baseball is a game played by humans and even if it weren't, there are a large number of variables that don't go into the simple analysis.

For example: The members of the defending team adopt fielding positions based on a maximum potential for fielding a hit ball. But if there is even a threat of a stolen base attempt, the defense must change their positioning accordingly, affecting their ability to field a ball put into play.

If a player does make an attempt to steal a base, at least one defender must begin to change their positioning before the hitter has even had a chance to hit the ball. If they do not, they will not make it to the base in time to receive the throw from the catcher and either the throw will not occur or it will go out into the outfield and the runner may advance another base. Alternatively, the hitter may actually hit the ball and the ball may go to an area that it is statistically likely to go, where a defender would have been but for the stolen base attempt. What was to be an out is now a hit and the runner, having a head start because of their stolen base attempt, is able to advance further than they normally would have been able to. Because the hitter hit the ball, this situation does not get recorded in the statistics as a stolen base attempt!

Baseball is really a fascinating game to think about!

> For example: The members of the defending team adopt fielding positions based on a maximum potential for fielding a hit ball. But if there is even a threat of a stolen base attempt, the defense must change their positioning accordingly, affecting their ability to field a ball put into play.

Yeah, that was the biggest flaw I spotted in the analysis of base-stealing: it doesn't seem to capture effect of the threat of base stealing on the defense's behavior, which is very probably non-zero and in favor of the offense. If you never, ever steal, and the defense knows that (someone'll notice before long), they can play better defense against the batter. It may still work out that a never-steal rule still provides better outcomes (by a smaller margin), but I'm guessing "rarely steal" ends up being the better guideline, overall.

If that's true, then I believe it means that the defenders are overcompensating for stealing. As I understand it, in equilibrium you'll have the feature that the defense cannot benefit by guarding steals less closely in exchange for better fielding position.

If trying to steal loses bases, then the defense could spend less effort preventing steals, and more effort fielding.

This principle comes up a lot: if you get into every college/job you applied to, then you probably didn't apply to enough schools/jobs, unless 1) you didn't want to go to Harvard/AppAmaFaceGooSoft, 2) you got in to Harvard/AppAmaFaceGooSoft, 3) you couldn't afford the applications.

He briefly addressed this in one of the appendices:

"Another reason to sac bunt (or bunt in general) is that the tendency to sometimes do this induces changes in defense which make non-bunt plays work better."

It apparently changes the probabilities slightly, but not enough to change the overall conclusion.

So how would this show up in statistics since 2012? Fewer Errors?

Yes, I would expect that a drop in stolen base attempts would lead to a drop in errors by catchers.

Looking at stats from 2000-2017, total errors underwent a steady drop from ~3400 in 2000 to ~2800 in 2017.

On the other hand, it is not entirely clear that teams stopped stealing bases starting in 2012. Yes, 2015-2017 were far below average, but so were 2003-2005.

http://www.fangraphs.com/

A lot of those moneyball decisions seem to have very marginal impacts, and I feel like the differences in team quality across the league were large enough that those subtle statistical advantages didn't matter very much. Moneyball only became a big thing after the luxury tax was implemented when a lot of teams were basically at parity in terms of player ability and small tactical advantages suddenly became meaningful.

Surely the players' individual ability to steal a base would play into this?

There are nine innings, during half of each of which one team plays offense and the other plays defense. They switch for the remaining half of each inning.

The offense is permitted three "outs" in their half of each inning (after which the teams switch roles, or the next inning commences).

There are four bases, the first three of which may be occupied by a member of the offense. Bases are ordered. Players may advance directly from one base to the next by "stealing". This comes at the risk of an out, which results in losing occupation of a base entirely.

A player which reaches the fourth base scores a "run" for the offense and no longer occupies a base. Runs (and only runs) count toward the final score.

One player from offense is always "at bat". That player has a chance to occupy a base (not necessarily the first); failure to do so results in an out. During this process, the other base occupants may (be forced to) advance bases, possibly scoring runs or losing bases and gaining outs in the process. (The particulars of this are not relevant to the article, but there is a fun story about the process here [1].)

Rather than permit the player at bat the chance to advance potentially several bases, the defense can "walk" the batter by granting them uncontested occupation of first base.

Similarly, rather than permit the defense to prevent any base advancement, the player at bat can choose a "sacrificial bunt" ("sac" bunt) which, properly executed, nearly guarantees that players currently occupying bases advance one base (or even score), while the player at bat (and only that player) is called out (and thus does not advance). SPOILER ALERT. This action is key to the plot in a particular episode of Deep Space 9 [2].

[1] http://www.espn.com/mlb/story/_/id/20294816/skunk-outfield-h...

[2] http://memory-alpha.wikia.com/wiki/Take_Me_Out_to_the_Holosu...

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