Police investigators are trying to figure out what caused a traumatic brain injury to a drunken man who was found in the South of Market district Friday.
About 9:30 p.m., police said, officers responded to a report that the 37-year-old man was bleeding from the head in the 1000 block of Mission Street, between Sixth and Seventh streets.
The victim "appeared to be under the influence of alcohol," police said.
The man was reportedly transported to San Francisco General Hospital with a wound to the back of his head that is considered to be life-threatening.
Police have not released the victim's name. Investigators have released few details about how the man became injured, but called the incident "suspicious."
Anyone with information is encouraged to call the Police Department's anonymous tip line at (415) 575-4444 or to send a tip by text message to TIP411 with "SFPD" in the message.