An annual party in a Southern California college town turned into a riot when members of the 15,000-person crowd began throwing bricks at police officers, lighting fires, and apparently stabbing each other.

The town, Isla Vista, is home to the University of California Santa Barbara, and the birthplace of Floatopia, an annual ocean party that got shut down in 2009 thanks to crime and the environmental impact of tens of thousands of drunk people partying on a half-mile stretch of beach.

Floatopia was replaced by the street-based Deltopia, which swelled to 15,000 attendees this year.

Police say the trouble began when a police officer was hit in the face with a backpack filled with large bottles of alcohol. The confrontation escalated as people apparently began throwing bricks, glass bottles, and beer cans while police sprayed pepper spray and tear gas and launched flash bang grenades and foam projectiles back at them. According to reports, Santa Barbara police also employed an armored SWAT vehicle.

People also began ripping up stop signs, lighting fires, and trashing cars. A police spokesperson said they had reports of a stabbing earlier in the day and found several people carrying weapons. This is apparently common in Southern California.

At the end of the battle, about 100 people were arrested, 44 were hospitalized (nearly all were drunk), five cops were injured, and everyone else had a sick time, bro.