Medics responded to the 500 block of Brannan Street about 10:39 p.m. on reports of a man on the ground suffering from a seizure, police said. The 24-year-old victim was unconscious and taken to a nearby hospital.
After an initial examination gauging the severity of the head injury, he was transferred to a second hospital where he remains unconscious and in critical condition, police said.
The examining physician told police that the victim sustained blunt force trauma to the left side of his head.
It's unknown if he was a victim of assault or somehow injured himself, Newman said.
Investigators are canvassing the area for surveillance footage that may have captured the incident and will also be checking 911 phone logs for any indication that there may have been an assault reported, Newman said.