Woman suffers brain injury after S.F. bus feud spills into street

CHICAGO, IL - SEPTEMBER 28: Crime scene tape secures a shooting scene where 5 people were reported to have been shot, including an 11-month-old infant, on September 28, 2015 in Chicago, Illinois. Chicago, like many major cities in the United States, has experienced a surge in shootings this year. (Photo by Scott Olson/Getty Images) less CHICAGO, IL - SEPTEMBER 28: Crime scene tape secures a shooting scene where 5 people were reported to have been shot, including an 11-month-old infant, on September 28, 2015 in Chicago, Illinois. Chicago, like ... more Photo: Scott Olson, Getty Images Photo: Scott Olson, Getty Images Image 1 of / 1 Caption Close Woman suffers brain injury after S.F. bus feud spills into street 1 / 1 Back to Gallery

A 55-year-old woman was hospitalized with a life-threatening brain injury after she got into an argument with two people on Muni bus that apparently spilled into a street in San Francisco’s Mission District and turned physical, police said Friday.

A man and a woman got into an argument with the victim, who was not immediately identified, on Muni’s 9-San Bruno bus around 7 p.m. Thursday, witnesses told police.

The three continued to argue as they got off the bus in the 300 block of Potrero Avenue, police said. Witnesses in the area heard yelling and then saw the woman on the ground unconscious, department officials said. Police are investigating the incident as a case of battery.

The woman was taken to San Francisco General Hospital, where she was being treated for life-threatening injuries, police said.

The two people fled the scene on foot, police said.

No arrests were made, and the investigation is ongoing.

Hamed Aleaziz is a San Francisco Chronicle staff writer. E-mail: haleaziz@sfchronicle.com Twitter: @haleaziz