Chaotic video shot in Tacoma, Washington state, shows the moment a police car was driven into a group of people who had gathered at an illegal street race.
Video shows a confused scene, as the car ploughs into up to 30 people in downtown Tacoma.
Police were responding to reports of street racing and blocked streets.
"People were messing with the cops, yelling at the cops, shouting at the cops, and then the car reversed and drove full speed into the crowd," Cory Le, who filmed the video, told Reuters.
Police told Reuters the officer had been concerned the crowd would smash windows on his car.
One person was hurt and the incident is being investigated.