Scientists say there are real psychological answers.
Part of it is mob behavior - people lose inhibitions when they're part of a big crowd.
Consuming alcohol escalates that loss of inhibition.
Fans also lose self-awareness, and don't really notice what they are doing.
Rabid fans may also identify so much with a team that throwing a rock becomes their mental equivalent of throwing a touchdown pass.
Evidence of that may have come outside the Michael's Craft store on Broad Street.
Young men who had dismantled and brought down a traffic light hurled it into the store's glass window, shattering it.
Ironically, fans of winning teams actually tend to riot more than fans of losing teams.
That might be driven by testosterone - the male hormone rises more after victory than defeat.