This fight occurred on the Muni Stockton route (the 9 i think) just before the stockton tunnel. As you can see, a simple argument about seat-hogging quickly turned into a full blown brawl. It's pretty clear who threw the first punch, you can see the bus' serial number, and the exact time in the video.
Oct 14, 2011
of fight on bus in chinatown
Fight on SF Muni Bus in Chinatown