Police say two men were arrested as some of the people protesting the police shooting of Alfred Olango became destructive and violent.
El Cajon police say between 50 and 75 protesters were in the streets blocking traffic on Thursday night until they used pepper-spray balls to break up the crowd.
Some protesters fought with drivers angry about the blocked road, breaking car windows and in once case knocking a man off his motorcycle.
Some threw bottles at police in riot gear.
Police say a 19-year-old man and a 28-year-old man were arrested for taking part in an unlawful assembly. Their names were not released.
It was the third night of protests over the death of Alfred Olango, who was killed on Tuesday after pulling an object from his pocket and pointing it at police.