The incident was reported at around 9:30 p.m. on Haight Street near Buena Vista Avenue West.
A 30-year-old man who walked out of the park was cut in the leg after he was confronted by another man with a fixed-blade knife.
The suspect, believed to be between 20 and 30, started a verbal fight and then pulled out the knife and stabbed the victim in the leg, according to police.
The man was taken to San Francisco General Hospital with injuries not considered life-threatening, according to police.
The suspect was able to get away and as of Monday morning had not been caught, police said.