Protesters in Sacramento, California blocked a motorway and basketball arena over the killing of an unarmed black man.
Scores first gathered at the city hall, holding signs and urging action.
The protests were sparked by the release of police video showing the killing of Stephon Clark, 22.
Police shot Mr Clark about 20 times on Sunday night in the backyard of his grandparent’s home while responding to reports of break-ins in the area.
Officers said they thought Mr Clark had a gun, but none was found at the scene – only a mobile phone.
His death is the latest in a string of police killings of black people that triggered mass protests and rekindled debates about race relations in the US.
Officers confronted and killed the 22-year-old in his garden, shouting “Gun, gun, gun” and opening fire after purportedly asking him to show his hands.
Each officer shot 10 bullets, according to the Sacramento Police Department.
The local Black Lives Matter campaign group announced plans for protests on Thursday after watching the footage.
After the release of the video late Wednesday night, protesters marched into Sacramento city hall at 15:00 local time (22:00 GMT) on Thursday.
The demonstrators then marched to Interstate 5, reportedly standing in front of vehicles chanting, “Don’t shoot, it’s a cell phone.”
The motorway was blocked in both directions and caused mile-long traffic jams.
The protesters then moved to the Golden 1 Centre, where the Sacramento Kings were scheduled to play the Atlanta Hawks at 19:00.
Arena security teams blocked entrance to the stadium, leaving protesters and ticket holders outside.
Forty minutes after the planned start time, the Kings announced they would not allow in any more spectators.
Only about 2,000 of 17,000 ticket holders managed to take their seats before the game began after a delay.
Police in riot gear arrived at the arena shortly after the protesters, but there were no arrests and no violence.