Critical Mass window smasher was wearing T-shirt advocating non-violence

A Critical Mass cyclist who attacked a Zipcar with a metal bike lock was wearing a shirt that said, "Non-violence is our strength." A Critical Mass cyclist who attacked a Zipcar with a metal bike lock was wearing a shirt that said, "Non-violence is our strength." Photo: YouTube / Bike42363 Photo: YouTube / Bike42363 Image 1 of / 23 Caption Close Critical Mass window smasher was wearing T-shirt advocating non-violence 1 / 23 Back to Gallery

Police in San Francisco continued to search Tuesday for a Critical Mass cyclist who smashed a Zipcar driver’s window with a metal U-lock on Friday while wearing a T-shirt reading “Non-violence is our strength.”

The unidentified assailant landed repeated blows on the vehicle and shattered the driver’s side window, coming within inches of hitting a woman behind the wheel in the head.

The back of the cyclist’s T-shirt was emblazoned with the quote attributed to famed California labor leader Cesar Chavez, who once said, “in some cases non-violence requires more militancy that violence.”

The run-in happen after a group of cyclists, riding the wrong direction down Marina Boulevard, surrounded the woman’s Subaru station wagon just after 8 p.m. Friday in San Francisco’s Marina District. Two of the riders captured the incident on video, which YouTube user Bike42363 cut together and posted online over the weekend.

The driver never filed a police report after the incident, but San Francisco police determined the situation warranted an investigation and are trying to track down the cyclist and the driver to get their accounts of the run-in.

Zipcar said it was aware of the incident but wouldn’t comment on the matter.

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