The Los Angeles Police Department is investigating a scuffle between police officers and some bicycle riders participating in a protest Friday night, officials said.

Part of the incident was captured on a handheld video camera and posted on YouTube with the title "Hollywood Cops Attack Bike Riders."

But the 1-minute, 31-second clip does not show clearly what happened.

Hundreds of cyclists rode en masse through Los Angeles to protest BP for the ongoing oil spill in the Gulf of Mexico. On Hollywood Boulevard, as dozens pass the camera, a police officer near the sidewalk in the background can be seen kicking once at a passing rider. "What the ... was that for?" a voice near the camera shouts.

Then the clip seems to show at least two officers converging on the person shooting the video. The screen goes black. When the picture reappears, the camera is on the ground angled up toward the officers, whose clubs are drawn. One policeman says "Get up" as another orders, "Get down."

"What'd I do?" a man can be heard repeating.

A statement released Saturday by the LAPD said an investigation has been launched in response to "a complaint filed by representatives of the L.A. biking community."

The incident occurred at 9:30 p.m. while officers were issuing citations to riders who had failed to stop at red lights, the statement said.

Paul M. Weber, president of the Los Angeles Police Protective League, issued a statement cautioning against a "rush to judgment."

"It is always important to remember that home video, shot from a distance, from one angle and in the dark, and not at the beginning of the incident seldom tells the whole story," the union's statement said.