It may in fact be considered assult...........BUT............he who wins the fight usually is the one in jail. Is it fair? NO, is it legally by the book? NO. Is it right? NO! But that is how it is! I have spend a few nights in jail for fights that I DID NOT start, even with witnesses to the fact. But when you win, the police see it as if you were the aggressor and your butt is in jail. The difference is with Celebs they will almost always get the benefit of doubt. With a working class guy there rarely is any innocent until proven guilty, it is guilty until proven innocent.
I think the fans that pull this crap should be punished as hard or harder than the players. But when you are a professional you are expected to have a higher level of self control than say a drunk fan. That is why the security at games is watching the fans, not the players.
100% I see your point, but it isnt as black and white as, I was assualted so I have a right to fight back. I most cases the way the law reads, if the threat has stopped you must also. So a thrown beer would not constitute a continued threat that would "legally" justify using force.