RANCHO CUCAMONGA, Calif. -- A California Highway Patrol vehicle appears to knock down a motorcycle rider in Southern California in a video streamed on Facebook on Sunday afternoon.
CHP officials said the collision happened "for unknown reasons" after a pursuit along Interstate 210.
The man hit by the patrol vehicle has been identified as 26-year-old Raul Martinez.
A CHP officer had been pursuing him along eastbound I-210 as he rode a blue 2016 Yamaha R6, officials said.
The pursuit then went from the freeway to surface streets, which is when the Facebook video starts to capture the officer chasing after Martinez.
In the video, dozens of bikers are seen stopped when one motorcyclist comes into view followed by a four-door Dodge CHP vehicle.
The CHP vehicle, which had its siren on, appears to swerve to the right, causing the rider to topple onto the ground.
The incident happened in the middle of a wide-scale motorcycle event advertised in a flyer published on, and since deleted from, Facebook by Sonia Villalobos.
It described the gathering as a memorial event called the "Fallen Brother Ride," organized by a group called Elite Bikerz Inland Empire.
The post suggested the ride started in the City of Industry about noon.
The group that was stopped rushed to the crash, with one of them heard yelling, "You pushed him. You pushed him down. I have it on camera."
Several others are heard screaming as they gathered around the CHP officer.
The video shows the officer handcuff Martinez. At one point, the official is seen pushing away another person touching the motorcycle on the ground.
In a news release, CHP officials gave an account of the moments leading to the incident caught on video.
Officials said the CHP officer was in pursuit of Martinez on eastbound I-210 when Martinez used the right shoulder to ride past a vehicle entering the freeway.
He then started to yield to the right shoulder on his motorcycle before continuing to drive down the freeway at "a high rate of speed" as he fled from the officer, officials said.
The pursuit exited the freeway and traveled through surface streets. Some time after that is when the collision happened.
"For unknown reasons, the left side of the Yamaha made contact with the right side of the patrol vehicle on 19th Street west of Carnelian Street," CHP officials said in a news release.
"The impact caused the rider to be ejected to the ground."
But a witness to the incident who did not want to be named said the bike appeared to be slowing down to pull over just before the crash.
"I thought it was inappropriate because the guy was pulling over and he was abiding to what he was supposed to do," he said. "And he hit him, the guy took a really good spill."
Martinez suffered minor injuries and was taken to a hospital for treatment before being booked on suspicion of felony evading, according to CHP.
The witness said he also became concerned for the CHP officer after a throng of "at least 200" riders surrounded him after the collision.
"They all swarmed around the police officer and they were revving their engines really, really loud," he said. "I mean, you couldn't hear anything. What really bothered me was that the police officer had no backup."
In the video, the person who took the video appears to leave the scene along with the other riders after surrounding the officer when he begins arresting Martinez.
Some of the riders said the officer used excessive force and that they plan to take legal action against CHP.AlertMe