Officers responded at 7:40 p.m. on Oct. 10 to a report of an attack at the Van Ness station in the 1400 block of Market Street.
According to police, the suspect tried to go through the pay gates at the station with his bicycle when the agent, a 55-year-old man, told him bikes were not allowed in the station.
The suspect ignored the agent and lifted the bicycle over the railing, then jumped over the railing himself and started walking toward the train platform, police said.
The agent followed the suspect to the platform when the suspect suddenly turned around and began punching and kicking him. He was knocked to the ground, then got back up and was punched again until he fell back down, according to police.
The suspect then fled out of the station and was last seen at the northeast corner of Van Ness Avenue and Market Street, police said.
The victim was taken to a hospital to be treated for serious injuries. He has since been released but has been unable to return to work, according to police.
"To have a station agent attacked just for doing their job is unconscionable," John Haley, SFMTA director of transit operations, said in a statement. "We need the help of our riding public to bring this individual to justice as soon as possible."
Surveillance video of the suspect was captured that evening and was released by police today.
Anyone who recognizes the suspect or has more information about the attack is asked to call the Police Department's Muni task force at (415) 832-8338. People wishing to remain anonymous can call (415) 575-4444 or send a tip by text message to TIP411.