If that’s the case then the increase would be seen in the NHL where there is a history of fights and enforcers but not e.g in the Swiss or Swedish leagues where there isn’t. But concussions are up across the board.

The more reasonable explanation for more head injuries is the game is faster (much fewer hookings, for example) and a focus on speed and skill over size and strength.

There just is no “I can’t punch this guy in the face so I’ll give him a cheap blindside to the head”. The stats doesn’t support the hypothesis.