Demonstrators threw rocks and bottles at LAPD officers as police and protesters squared off in downtown Los Angeles late Thursday night.
At least 20 arrests were made and four officers were injured.
The confrontation began after the Occupy L.A. movement urged supporters to gather at a monthly event called ArtWalk. Demonstrators arrived to protest the apparent arrest of people who had written on the sidewalk with chalk during previous events.
The movement advertised the “Chalk Walk” event on its Twitter feed, saying, “we will be handing out free chalk for free speech.”
Shortly before 10 p.m., the LAPD issued a tactical alert, and sent hundreds of officers to the demonstration at Spring and 5th streets.