A man appearing to be walking though an airport in San Francisco with his camera recording,  attempted to make small talk with a cop, possibly to file a complaint.

Derek Youmans then offered his hand, but officer Keith Parker refused to shake it.

Youmans then appeared to slap the cop on the shoulder, a chummy half-hearted slap you do with friends or co-workers that never causes a violent reaction.

But that made the cop fear for his life, which is why the cop pounced on him and arrested him.

No further details at this time, but we will updating.

UPDATE: It turns out, Youmans did not touch the cop prior to being attacked.