It’s just not that simple. You aren’t repeatedly being hit in the head playing football. Even the linemen who have aggressive contact each play aren’t banging

It’s just not that simple. You aren’t repeatedly being hit in the head playing football. Even the linemen who have aggressive contact each play aren’t banging their heads together, they are using their hands. The helmets are largely protecting against incidental contact. Head trauma comes from rapid changes in momentum that cause the brain to bounce around inside the skull. Those from “horse collar” tackles, which are illegal now. Those from intentionally or unintentionally having helmet to helmet contact, which is also illegal. Virtually every type of helmet hit is penalized at this point. Soccer headers are probably much worse I would imagine.