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What happened at 555 California Street in San Francisco, known as Black Rock to skaters, began as a fairly common confrontation.

A group of skaters descended upon a location, one that had been scouted as ideal for executing new tricks, and they faced security. A guard asked the group to leave, and a dispute ensued.

Many of these encounters are captured, glorified and posted online by skateboard media, athletes and fans.

But in this case, things quickly got out of hand. It was all caught on camera. Minutes after a group of skaters arrived at 555 California Street, Dan Jansen, a security guard who had worked at the building for 15 years, asked the skaters to leave and placed steel barriers in their way. The skaters moved the barriers, and an increasingly tense show of force from both sides followed.