Skateboarders and police have clashed in the US city of San Francisco during an informal “hill bombing” competition, reports say.
Footage show a skateboarder and an officer colliding, sending the skateboarder flying into a police car.
Skateboarders threw bottles at police in riot gear but no arrests were made, the LA Times said.
Two skateboarders and the police officer were taken to hospital, a police spokeswoman said.
There were no details about their condition.
A crowd of several hundred people had gathered to watch the skateboarders descend a steep hill in Dolores Park in the city’s Mission district.
Some reports say the emergency services were called when a skateboarder fell at speed but others say residents were complaining that their street had been taken over.
After police arrived, witnesses said an officer intentionally leaned in to clip a speeding skateboarder with his shoulder, sparking anger among onlookers.
However the San Francisco Chronicle quoted a police officer as saying the collision had been an accident.
The confrontation lasted at least an hour. A police vehicle had a window broken and two vehicles were tagged with graffiti during the stand-off, a spokeswoman said.