Steven Jenkins, 39, was booked on two counts of assault likely to produce great bodily injury, and two counts of elder abuse, the San Francisco Police Department said in a statement.
Jenkins is accused of attacking an 83-year-old Asian man on Wednesday morning in the Tenderloin District before being chased by a security guard on foot.
"As Jenkins was fleeing, he assaulted the female victim," police said in a news release. "The security guard was able to detain Jenkins until officers arrived."
Both assaults are believed to have been unprovoked, investigators said, adding that they are working to determine if racial bias was a motive.
RELATED: Coalition tracks increase in attacks on Asian-Americans
News video from the scene showed Jenkins bleeding and handcuffed to a stretcher before he was placed in an ambulance and transported to a hospital.
The female victim was holding an ice pack to her head and a wooden stick or paddle in her hand.
She told San Francisco station KPIX she had been leaning against a utility pole when the assailant punched her without provocation.
KPIX reported that the woman repeatedly said in Chinese, "You bum, why did you hit me?" and then turned to the crowd and said, "This bum, he hit me."
The attack came as reports indicate an increase in attacks against Asian-Americans over the last year during the pandemic.