Police found the victim, a 22-year-old San Francisco man, lying on San Francisco Municipal Railway tracks in the 1400 block of Taraval Street at about 12:40 a.m.
The man was unresponsive and bleeding from the head, police said. He was taken to San Francisco General Hospital in critical condition.
Police did not have an update on his condition this afternoon.
Three men -- Herman Yeung, 29, of Oakland, Michael Lien Hoa Ha, 26, of San Francisco, and Alex Tao, 27, of San Francisco -- were arrested at the scene.
Police said several witnesses told investigators that two groups of men, one of which included the victim, began arguing inside a nearby bar, the Dragon Lounge at 1355 Taraval St. The argument then continued outside.
The victim was apparently punched and then kicked in the head while on the ground, police said.
Yeung, Ha and Tao were booked into jail on suspicion of attempted murder and assault with a deadly weapon, police said.