Two men - a bearded white man who said he was 67 years old and a younger black man - can be seen on the video arguing on the transit bus Monday afternoon.
"The white guy was asking the black guy for a shoeshine," Iyanna Washington, the student who shot the video with a small camera, told CBS station KPIX. "And I guess the black guy took it as a racist comment, like, 'Why's a black guy have to spit shine your shoes?'"
After several minutes of back-and-forth yelling, the older man moves to the front of the bus, though the argument continues. Eventually, the younger man follows him.
"I guess he hit him across the face once," Washington said. "And then the white guy stands up and lets loose."
The unidentified older man unleashed a flurry of punches that bloodied the face of the younger man, who was later found to have sustained a broken nose, transit spokesman Clarence Johnson said.
The older man exited the bus but remained in the area, screaming and kicking at a newsstand. He eventually surrendered when police showed up.
Both men were taken to the hospital. Johnson said the older man was off his medication.
Video shows Washington grabbing the older man's bag and carrying it to the back of the bus while somebody says, "Go through that." But Washington told KPIX that she didn't steal anything.
"Why would I steal the guy's bag?" she said. "I picked the bag up, I placed it on the seat and that was the end of that. When I got off the bus the bag was still on the bus."