Police reported three separate stabbings took place between noon and 2 p.m. in the vicinity of the Montgomery and Market streets. All three victims suffered non-life-threatening wounds, police spokesman Sgt. Neville Gittens said.
Gittens said the motive for the attacks was unknown.
In the first incident, shortly after noon, a 17-year-old San Francisco boy was stabbed on the left side by a man who grabbed the boy's cell phone in the Montgomery Street Bay Area Rapid Transit station.
In two separate incidents around 2 p.m., a 38-year-old Illinois man was stabbed at Jessie and First streets, and a 40-year-old San Francisco man was stabbed in the Montgomery Street Muni station, police reported.
The Illinois man reported that his assailant was walking in the opposite direction and deliberately bumped into him. He then discovered he had been stabbed.
The Muni station victim reported being stabbed in the thigh from behind as he rode the escalator.
As the reports were broadcast on police radio, officers noticed a man matching the suspect description on a Muni F-line streetcar at Sixth and Market streets, and detained the suspect.
The man, 25-year-old Duwayne Hyman, was found with a steak knife in his back pocket and was arrested without incident, police reported.
Hyman remains in custody, charged with assault and robbery, according to police.