The attack was reported at 11:54 p.m. near the intersection of Bosworth Street and Brompton Avenue.
The 28-year-old victim was approached from behind by three male suspects who demanded her purse. The victim refused to comply and began to struggle with the suspects over the purse, according to police.
The victim then lost control of the purse and fell back, striking her head on the pavement. She fractured her skull and was taken to San Francisco General Hospital to be treated for her injuries, which are considered life-threatening, police said.
The suspects fled with the purse and had not been found as of this morning. Anyone with information about the case is encouraged to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.