Fans were throwing everything that wasn't nailed down. An official got hit with a water bottle that spun him around. People were throwing cups of ice into players face. The guy that threw the cup of ice which started the whole thing grabbed artest from behind and started to sucker punch him. Jermaine O'Neal was attacked and punched repeatedly by some big black guy with credentials on. You better take a closer look at the replays.
You are correct and the fans should not have done that. Nonetheless it would never have gone that far if a couple players had not ran into the stands and attacked a fan. Turns out the fan who was attacked did not throw the beer. Innocent fans could have been hurt very bad by these huge men going ballistic in the stands. Maybe even a child. Look at the grandma laying on the floor.
Oneil (I am pretty sure he was the player) landedtwo huge punches especially the running punch that connected with the fan who had gone on the court and had just been punched by Artest. It is somewhat of a miracle that running punch did not connect very well and break his jaw or even kill him by cracking open his skull when his head hit the court.
I think he was very lucky and he could have easily been paralyzed with a broken neck.