Any, and I mean any, hit in your head can lead to nasty consequences in the long run. You don't need to be KOed to be worried about your brain. Concussions and brain trauma still being a mystery for the scientific community.
8.000.000.000 of humans as of today. We are a stupid by nature specimen, who's surprised this kind of stuff happens. There's always someone who's going to do it.
I'm a boxer myself and I'm pretty aware of all this.
Anyway, smoking, preservatives, glyphosates, colorants and all those poisonous stuff are in our table almost daily and they eventually have crazy consequences for our health. I suppose we humans are doomed from day one.