It’s all fun and games until 15,000 people show up and somebody starts throwing rocks and bottles.

William M. Welch of USA Today reports.

100 arrested after Calif. spring break party turns violent

Six police officers were injured, more than 100 people were arrested and dozens were hospitalized when a large spring break party near the University of California-Santa Barbara turned into an unruly civil disturbance, officials said Sunday.

Police used tear gas and what they described as “foam projectiles” to regain control of the rock and bottle-throwing crowd.

An estimated 15,000 people attended the all-day party Saturday at Isla Vista, a beach community that borders the UC-Santa Barbara campus, the Santa Barbara County Sheriff’s Department said. The annual spring party is called “Deltopia.”

“Our community is in shock today over what happened last night,” Kelly Hoover, spokeswoman for the Santa Barbara County Sheriff’s Department, said. “It’s unbelievable to see people throwing rocks, bricks and bottles and beer cans at law enforcement officers.”

Violence erupted around 9:30 p.m. after a university officer was hit in the face with a backpack containing bottles of alcohol, the department said.

One person was charged with assault with a deadly weapon for allegedly striking the campus officer, and 18 people were charged with refusing to disperse, Hoover said. She was unable to say if any were still in custody Sunday evening.

“An unlawful assembly was declared and soon afterward the situation escalated into a major disturbance, emergency situation,” Hoover said.

Law enforcement officers, including some from nearby jurisdictions, used chemical agents and foam projectiles to disperse the crowd, she said.

At least five sheriff’s deputies were injured, including one hit in the face with a brick and two struck by bottles. All officers who were injured were doing well and out of the hospital, although one still faces surgery on a hand, she said.