Antonio Brown's biggest red flag on his scouting reports coming out of college was his character. His behavior may or may not have anything to do with that concussion.
And AB wasn't playing flag football in college/HS. Certainly not the first big hit he took, either. But I agree, this one seemed to really mess him up.
There's AB before the hit and AB after the hit.
youtube link to the hit: https://www.youtube.com/watch?v=o8iFSP_S5h8
most times you think -- concussions are a matter of repeated effect -- but one can change your life drastically.