Critical Mass event turns ugly in the Marina district

A YouTube video showing an altercation between Critical Mass cyclists and a driver in San Francisco’s Marina District on Friday August 28, 2015. A YouTube video showing an altercation between Critical Mass cyclists and a driver in San Francisco’s Marina District on Friday August 28, 2015. Photo: YouTube / Bike42363 Photo: YouTube / Bike42363 Image 1 of / 18 Caption Close Critical Mass event turns ugly in the Marina district 1 / 18 Back to Gallery

A YouTube video showing a tense altercation between Critical Mass cyclists and a driver in San Francisco’s Marina district captured a man pounding a woman’s Zipcar and smashing her window with a bike lock.

The video was purportedly shot Friday night at 8:16 p.m. on Marina Boulevard at Lyon Street during a Critical Mass bike ride.

About a dozen cyclists were seen riding against traffic on Marina Boulevard when one person stopped in front of a dark-colored station wagon and yelled, “Hey! Stop that! No, no, no, no, no.”

The man’s buddies then surrounded the car.

“You ain’t going nowhere,” another man is heard saying.

“You f— hit my bike,” the original rider shouted to the driver.

“Selfish, bitch,” someone else yelled.

The cyclists then lectured the Zipcar driver for several minutes while Harvey Danger’s “Flagpole Sitta” blared from a speaker attached to another cyclist’s backpack.

Apparently the driver had enough. She backed up and tried to drive around the pack only to be blocked again. Meanwhile, several other drivers appeared to keep a safe distance from the altercation.

Finally, the Zipcar slowly pushed past the group while one rider landed four blows on the side of the car with a U-lock, smashing the driver’s side window.

San Francisco police officials initially said they were aware of the video, but were not looking for the lock-wielding man because apparently no police report was filed.

“If a victim does not file a report, there is no crime that we can charge the person with,” Officer Albie Esparza, a San Francisco police spokesman, said Monday. “The person needs to file a report for an investigation to be initiated.”

Esparza later said the department had assigned an investigator to the case and would be working with Zipcar to look into the incident, but added, “we are hoping to speak with both parties involved to obtain a full picture of what happened.”

A Zipcar spokeswoman said she was aware of the incident and that “the well-being of anyone involved is our top concern,” but she declined to comment further on the incident or identify the driver.

A YouTube user who goes by the name bike42363 posted the video Saturday. It had more than 14,000 views by Monday afternoon and was inspiring an enthusiastic discussion in the comments section.

“Wow. You guys are pieces of s— for doing that,” YouTube user One TwiztidMunky wrote in part referring to the rowdy Critical Mass cyclists.

“It was a protest Einstein,” user drie wiel fired back.

Critical Mass is a monthly protest ride that happens on the last Friday of every month in San Francisco. The demonstrations began in the city in 1992 but are now held in nearly 300 cities around the world, according to the organization’s Web page.

On its website, SF Critical Mass tells participants “Don’t ride into oncoming traffic on the wrong side of the road” and “Don’t pick fights with motorists, even if they’re itching for one.”

Evan Sernoffsky is a San Francisco Chronicle staff writer. E-mail: esernoffsky@sfchronicle.com Twitter: @EvanSernoffsky

Video

To see the video of a Critical Mass rider attacking a motorist, go to http://bit.ly/1hP7QtT