The problem with these studies is that they gather their stats from doctors. I have no idea about Rugby, but American football has a very real culture of hiding concussions at all costs. If the only statistics they're using are from team doctors, they are GROSSLY underestimating the number of concussions in an average football season.

There's a belief that the average lineman is suffering some form of brain damage on pretty much every down they're in the game.

https://www.thebiglead.com/posts/linemen-are-more-prone-to-c...