The incident was reported at 11:39 p.m. at Third and Harrison streets four blocks from the ballpark. San Francisco police detained three people after the incident, but no arrests have been made.
The victim reportedly attended the game with his father and brother who were wearing Dodger blue when the fight broke out. The victim was not wearing any baseball related gear.
The Giants won Thursday's game 6-4.
The Giants-Dodgers rivalry is one of the most competitive in American baseball and it stems from the time when both teams played in the New York City area.