She was responding to a call about a man making racially motivated threats in Chinatown, only to be attacked by the man herself.
Multiple witnesses jumped in to save her.
One witness called 911 to report the man, identified by KGO-TV news anchor Dion Lim as Geraldo Contreras.
He was allegedly making threats the day before, saying he "specializes in killing Asian people."
WATCH: Full surveillance video of man's attack on SFPD officer in Chinatown
Video shows the Asian female officer approach Contreras, tell him to turn around and put his hands on his head.
He obliged, but when the officer asked if he had any weapons in his possession, he turned around, shoved her and wrestled with her before pushing her to the ground. She was carrying a bean bag gun across her back, but was clearly unable to reach for it.
"He's a big guy, he was not letting go. He had a death grip on her. And he was not letting go," says Michael Waldorf, who had just finished eating dinner with his family at the R&G Lounge on Kearny Street.
"I saw it as an emergency. She needed our help and she needed it right away," he told KGO.
Waldorf and several other bystanders quickly jumped into action, tackling, hitting and trying to pry Contreras off the officer, who appears to be about half the size of her assailant.
According to documents obtained by Lim, Contreras has a record of prior arrests, including aggravated assault, elder abuse and assaults on officers in other parts of California. It's unclear if he was ever convicted.
Upon learning this information, Waldorf appeared stern, saying, "He should not be let out. Some people are not safe for society and he clearly is not. I know this is just a snapshot of a person's life, but you have to look at someone's record and make a judgement."
Sources tell Lim the officer sustained a bloody nose and minor injuries.
Correction: A previous version of this report misquoted Michael Waldorf, a witness who helped the policewoman. The article has been updated to reflect Waldorf's description of the attack as "a death grip."