Ignorant of the law? I don't know where you live, but around here it's ASSAULT to throw anything at anyone.
And I believe the chief of police in MI has said as much also.
If you could see my face, you would know it's blue right now. That's how many times I've said it -- the beer guy was wrong and should be punished accordingly. I've NEVER NEVER NEVER NEVER NEVER said he wasn't wrong or that he shouldn't be punished.
BUT, Artest was more wrong to leave the court, run into the stands, and to take matters into his own hands instead of allowing those in authority deal with beer guy. Force against another is only justified when it is used in self defense -- and then only to the extent necessary to stop the potential harm -- not any greater.
And just a technicality, but there likely was not an assault committed by beer guy. Assault is the fear of imminent harm. Battery is the suffering of the harm. Because Artest never saw beer guy wind up and throw the cup, there was no assault. Rather, beer guy battered Artest when he hit him with the cup. The terms are mixed up regularly.