At first, the below video seems like nothing special — it's a cab driver's dashcam, capturing what appears to be a peaceful fare in downtown San Francisco. Then suddenly, out of nowhere, violence.

It starts like any other cab ride, as the driver tells his passenger "If you're just going to BART, there's one closer, just straight ahead...That'll save you a couple bucks."

But moments after the passenger agrees to be dropped off an Civic Center Station, his demeanor changes, and he starts screwing around with...something.

The driver, who can apparently sense that something is amiss, asks "What do you got going on back there, brother?" A split second after that, the passenger appears to attack the driver with a padlock looped around his finger.

You can watch the entire thing here:

This video was posted today (so, we're obviously approaching it with a great deal of caution) by YouTube user "CognizantDissident." He or she writes:

"This man attacked my friend while he was driving a taxi in SF on Monday, March 30th. He mentioned living in Fruitvale within ten blocks of the BART station though this could obviously be a lie."

According to "CognizantDissident," the suspect is an Asian man, noting that "the video being at night was using infrared illumination and the coloring was bad and there is pretty bad red/reflective eye making the area around the eyes darken a bit and blur."

When we, like KPIX (who also posted the video today) contacted SFPD regarding the incident, a spokesperson said that they were aware of the video, but didn't immediately have any more details on the case.

However, "CognitiveDissident" appears to be indicating that a police report had ben filed, saying that "If you have any information about the identity of this man please contact SFPD @ 415 553 0123."