The Knicks know a thing or two about fan misbehavior. According to Newsday, in March 2003, an inebriated Calvin Klein "left his courtside seat and walked toward [Latrell] Sprewell, who was inbounding the ball. Klein then grabbed a stunned Sprewell by the arm and got off a few words before being ushered back to his seat by Garden security." Gawker has a hilarious photo of that scene.
After that incident, New York City passed a law banning fans from entering the court or field during professional sports events. In May of this year, a Totowa, NJ man became the first person to be prosecuted under the so-called "Calvin Klein law," when he ran onto the field during a Mets game holding a sign saying "Howard Stern, Here’s Johnny." According to the Queens Chronicle's coverage of the incident, the law provides for civil penalties between $1,000 and $5,000 for entering the court/field during a professional sporting event, and between $10,000 and $25,000 for making physical contact with a player.
In the wake of the Pacers-Pistons brawl, we can probably expect more cities to pass similar laws. Whether throwing a beer at a player while he's on the announcer's table would constitute physical contact, and whether the announcer's table would be considered part of the court/field, would probably depend on the wording of such a law. But under a Calvin Klein law, the chubby Pistons-jersey-clad fan who rushed the court would have gone home with a fine, in addition to the bruises he must have from getting clocked by Ron Artest and Jermaine O'Neal in the face.