Demonstrators must remain on sidewalks Tuesday night and will be arrested if they commit any crimes or block traffic, police said.
The zero-tolerance policy is a result of protests that began in the Crenshaw district of Los Angeles and in the city of Oakland after the acquittal of Zimmerman on Saturday.
In Los Angeles, Deputy Chief Bob Green, who heads the South Bureau, said officers were pelted with rocks as they stood by monitoring the Crenshaw protests on Monday night.
"Unfortunately we had this ... component that we have seen for three days, and we've seen these knuckleheads are spinning up that emotion, ultimately trying to have a confrontation," Green said. "I've tried extraordinarily hard not to."
Police said 14 people were arrested, primarily for failing to disperse, with one person taken into custody for inciting a riot.
Injury numbers were not immediately available from authorities in Los Angeles and Oakland.
Police said about 150 people split from the demonstration Monday at a Crenshaw-area park, running through the streets, jumping on cars, trying to break store windows and committing assaults. A Wal-Mart store was vandalized.
In addition, TV news helicopters showed some people kicking and punching others along a Los Angeles street, including two people sitting on a bus bench. A reporter and photographer for Los Angeles TV stations KCBS and KCAL were assaulted and transported to a hospital with minor injuries.
Los Angeles Fire Department spokesman Brian Humphrey said no one had suffered serious or life-threatening injuries as part of the protests.
In Oakland, demonstrators left a gathering at City Hall before briefly blocking Interstate 880, trying to march onto Interstate 580, throwing fireworks and assaulting a restaurant waiter with a hammer.
Oakland police used flash-bang grenades and made nine arrests for crimes including assault with a deadly weapon and vandalism.
A protester was injured by a police projectile, witnesses told the Oakland Tribune (http://bit.ly/18i9j1E ). Police were checking to confirm that incident occurred, said Officer Johnna Watson, a police spokeswoman.
The crowds and officer response in Los Angeles were much smaller than the city saw during the 1965 Watts riots that resulted in 34 deaths, and the 1992 riots that followed the acquittal of four officers in the beating of Rodney King.
More than 300 police officers responded to the Crenshaw demonstration. They were intentionally slow to directly engage protesters to allow a peaceful end to the demonstration.
Police said a core group of "troublemakers" included no more than 75 people most from outside the community. Police said a similar situation occurred in Oakland.
In Los Angeles, protesters were texting each other and using social media to direct what was essentially a crowd without leadership, Green said.
The department has an evolving relationship with the community and is trying to reign in violence without interfering with people who are legitimately trying to express their emotions over the Zimmerman verdict, Green said.
"There's this fine balance," he said. "There's this core group that just wants a confrontation, so our success is going to be discipline, restraint."
He pointed out, however, that the broader community has expressed to him that they want the violence to stop.
Earl Ofari Hutchinson, president of the Los Angeles Urban Policy Roundtable, a south Los Angeles-based community activist group said the department's response demonstrates its progress in dealing with the African-American community, though he said there's still a ways to go.
"If you notice last night, they didn't wade in with stun guns and billy clubs, shooting up the joint, which might have happened 20 years ago," Hutchinson said. "I think that's a sign they've learned a few things."
Los Angeles Police Commissioner John Mack, a former president of the Los Angeles Urban League, said the department has consistently reached out to community groups over the last years and slowly build a relationship of trust.
"It's important we don't get carried away and get so focused on the few, who in my opinion clearly were not a part of the organized group and had their own agenda," Mack said. "Quite frankly, I'm not so sure that all of them even cared about Trayvon Martin."