This had been going on for some time and it was obvious security wasn't doing anything to try to control the situation. Look, I am not an Artest fan and for the most part think he is a thug. But he had taken himself out of the situation and the fans decided in inject themselves in to it by throwing beer at him.
I won't defend the fan who threw the cup. He's a jacka** and should be appropriately punished. However, Artest retaliated -- he was not defending himself. There is a very distinct difference, and there should and will be consequences for his retaliation.