After witness reports suggested a police officer extended his left arm to collide with a skateboarder near Dolores Park on Tuesday evening, the San Francisco Police Department says it’s delving into an investigation of the incident and the handling of a confrontation with nearly 400 skaters. And, because this was a skateboarding event, there's plenty of video.

As the Chronicle reports, following tensions that flared for over an hour Tuesday between skaters and cops, the trouble all began with a pair of bad wipeouts, one of which, says the SFPD, occurred when a skateboarder and a cop simply collided, sending the officer to the hospital.

In a video of the crash shown above and below, the skater speeds past the officer, hits a patrol car, and flips over onto the street. As the crowd exclaims, the skater clasps his leg in pain. The patrol car had been parked in the middle of the street, and the skaters immediately begin yelling at the officer, blaming him for the collision.

The wipeout led to bottles and objects being thrown at officers and the officers donning riot gear, as the LA Times reported, all as skateboarders continued speeding down the Dolores Street hill as part of an unauthorized second annual event called "The Hill Bomb."

Mission Local reported that Jake Phelps, the editor of Thrasher magazine, was among several injured skaters. He was taken to the hospital for staples in his head from injuries you can see in the ABC 7 video below. Police say that emergency personnel were unable to reach Phelps quickly due to the size of the crowd.

San Francisco Police Officer Grace Gatpandan tells ABC 7 that activity near the park — she cited throwing of bottles, preventing medical care at the scene, and skating against traffic — constitutes unlawful behavior. No arrests were made, however.

Other witnesses, like Dina Boyer who spoke to ABC 7, describe a benign and happy scene leading up to the confrontation. "I saw skateboarders going down the sidewalk and the street and they were just having fun, screaming hollering and laughing, cheering each other on," she said.

Police Chief Bill Scott tells ABC 7 that based on allegations from both sides of the clash, the police department will examine videos from the scene including body cam footage to determine what happened. The incident came up at Wednesday's meeting of the Police Commission.

“Hill-bombing,” where skateboarders accelerate down steep inclines and compete for the fastest speeds, is a common practice in San Francisco. The contest on Tuesday held a cash prize, per the Chron. And though the scene smacked of past confrontations between skaters and police, witnesses say the collision with the officer is what caused Tuesday’s scene to get uglier.

Andrew Bahena tells the Chronicle that the officer involved in the collision stepped into the only available path for skaters to ride through after police blocked off the street. “Even if it was a collision, it was a collision that was contrived,” Bahena said. “The cops were being antagonized and he antagonized the collision. From there, things escalated really quick. Within 10 seconds of that kid going down, the skateboarders were hitting their boards on the ground and making noises.”

Many witnesses decried the heavy police presence, but several skaters at the scene exhibited pride that the event drew such a crowd. “We literally shut down Dolores Street,” one skater named Pete tells the Chronicle.

Previously: Ugly Dolores Park Confrontation Between Police, Skateboarders Ends In Multiple Injuries