Sometimes I feel hypocritical when watching football. In some ways it's modern day gladiators just with volunteers and not literally fighting to the death. It is not a matter of IF someone will get hurt, its a question of how many and how badly. Both teams have full medical staffs with an ambulance on site when its needed. They have carts to take players to the locker room because it is common and expected that players will be hurt so badly they are not able to transport themselves. They have an injury tent on the sidelines.
I don't think you need studies to know that getting hit in the head repeatedly is not good for you, but there are some out there.
Here is one that showed measurable cognitive decline in linemen even if they did not suffer a concussion (they did return to normal after the season was over) -
https://www.si.com/more-sports/2011/04/13/high-schoolconcussion I read another similar story a while ago (was not able to find it) where they did a test prior to, during, and at the end of the season and most linemen saw a marked decline on their test performance throughout the course of the season. Football was literally impairing their brains ability to function.