About 100 people were arrested and at least 44 were taken to hospital during a weekend college party in Southern California.
The violence broke out in the densely populated beachside community of Isla Vista on Saturday during the annual spring break party known as Deltopia, the Santa Barbara County Sheriff's Office said.
Sheriff's spokeswoman Kelly Hoover said things escalated after a University of California, Santa Barbara police officer was hit in the face with a backpack filled with large bottles of alcohol.
The authorities said some members of the crowd of 15,000 then began throwing rocks, bricks and bottles at officers, lighting fires and damaging law enforcement vehicles.
"It was an emergency situation where we had to call in mutual aid," Ms Hoover said.
"They have had civil disturbances before in Isla Vista, but it has been many years since something like this."
Police reported using tear gas, pepper spray and foam projectiles to disperse the surging crowd.
At least five more officers were injured in the brawl, including one officer who was hit in the face with a brick and two others who were both hit in the hand with bottles, sheriff's deputies said.
It was not immediately known yesterday how many people remain in custody or were still being treated at the hospital.
Earlier Saturday, authorities also responded to reports of a stabbing and found several individuals carrying weapons, Ms Hoover said.
Aside from those who were treated after the brawl broke out, nearly every person who was taken to hospital on Saturday had consumed excess alcohol, she added.
"It really was ridiculous," Ms Hoover said. "Deltopia attracts out-of-towners who come in and are not invested in our community and there are some who come to cause trouble."
The situation stabilised yesterday morning after sheriffs received back-up support from neighbouring Ventura County.
Isla Vista borders the university and is known for partying. The half-mile area has roughly 23,000 residents, of which 60% are students.