Police have arrested at least four people during a small but tense rally staged by a politically conservative group at the University of California, Berkeley.
The protest was led by Joey Gibson, leader of a group called Patriot Prayer, and supporters including Kyle Chapman, a self-described "American nationalist."
Counterprotesters got into shouting matches with supporters inside an "empathy tent" set up on campus and later in a city park.
Police said they arrested four people, including left-wing activist Yvonne Felarca, for battery and resisting arrest.
Three men were arrested on charges including possession of body armor, carrying a banned weapon and participating in a riot.
Gibson called for the rally after student organizers canceled a planned "Free Speech Week" this week that was to feature right-wing firebrand Milo Yiannopoulos.