Fullerton police were forced to dispel the crowd after a local news photographer was assaulted by a protestor.
Police Sgt. Jeff Stuart says Saturday's demonstration drew about 200 people.
Overall, 14 people were arrested. He says one person was arrested in the photographer's assault and two others were arrested after spray-painting an obscenity and an anarchist symbol on the intersection of Harbor Boulevard and Commonwealth Avenue. Ten were arrested on failure to disperse charges.
The last suspect was arrested and charged with robbery. Police say the suspect entered a local Stater Bros. store on the 300 block of Euclid Street and attempted to steal items from the store. When a clerk attempted to stop the suspect, he pushed the clerk to the ground.
Officials said they did everything possible to accommodate the protestors, but were forced to take action when demonstrators turned violent.
"All efforts were made in an attempt to accommodate the protestors: coordinating with organizers, providing barricades and blocking intersections for them," said Fullerton police Chief Dan Hughes.
Officers responded in riot gear to disperse the crowd.
The protest comes five days after two former Fullerton police officers were found not guilty in the death of a mentally ill homeless man. Kelly Thomas, 37, died days after a violent confrontation with six officers in July 2011.
The encounter was caught on surveillance video. Prosecutors said it showed officers abusing their authority and using unlawful excessive force. The defense says the officers were doing their jobs and were faced with a combative suspect.
On Monday, a jury found former police officer Jay Cicinelli and former officer Manuel Ramos not guilty on all charges. Ramos was charged with second-degree murder and involuntary manslaughter, and Cicinelli was charged with involuntary manslaughter and excessive force.
During a news conference on Tuesday, Thomas' father, Ron, and his attorney, Garo Mardirossian, said they're going ahead with a civil lawsuit to seek justice.
Fullerton police are reviewing video footage of Saturday's incident and say they have identified a number of additional suspects, likely leading to arrests in the near future.
CNS and The Associated Press contributed to this report.