This is oft-cited but before helmets, NFL players were dying at a pretty rapid pace [0], and this is before advanced strength and conditioning.
NFL players rush into each other at full speed knowing the risks. Why would that change if you removed protective padding that has been proven to do very little?
[0]: One such article on the topic: https://paleofuture.gizmodo.com/19-football-players-died-in-...
http://www.history.com/news/how-teddy-roosevelt-saved-footba...
Injuries were also caused by a lot of plays that are illegal today - flying wedges and various dirty blocks (clipping, chop blocks).
300lbs, running 5seconds for 40 yard, 2% bodyfat -- straight at you -- head down -- helmet first. Oh yeah. They trained on smashing into bags for this for 10 years.
Lots are a bit faster and around 230 or 250 lbs though.
https://www.inverse.com/article/37934-nfl-funded-study-brain...
Really? Because someone did just that in the AFC championship a week ago in order to (successfully) take out Rob Gronkowski.
Do NFL athletes really have 2% bodyfat? That's elite bodybuilding physique, and only sustained temporarily for competition. I find it hard to believe that football players can compete with so little fat.