A police sergeant getting viciously attacked by a transient overnight shot and killed her attacker, the Alameda County Sheriff’s Office said.

The sergeant was on routine patrol by herself when she spotted a suspicious person about 1:30 a.m. near the parking lot of a car dealership at Amador Plaza Road and Saint Patrick Way, said Sheriff’s spokesman Sgt. J.D. Nelson.

Within a minute of approaching the man, a known transient in the area with a history of arrests for fighting and drunkenness, he began punching her and knocked her to the ground. Nelson said the confrontation, which lasted about three minutes, quickly had the sergeant fighting for her life.

“”She got bloodied up. He tried to smash her head into the cement,”” Nelson said. “”She got free, took out her service weapon, and opened fire, killing him.””

The man, whose identity was not immediately released, was pronounced dead at the scene. The sergeant, who has more than 20 years experience, was taken to the hospital with serious but not life-threatening head injuries, Nelson said.

What precipitated the fight is under investigation; the sergeant has not been interviewed yet. Once she is released from the hospital, she will be placed on paid administrative leave pending a probe led by the district attorney’s office, which is routine in officer-involved shootings.