Denver was fatally stabbed during a fight reportedly between Dodgers and Giants fans after the game four blocks away from the ballpark.
San Francisco police gave few details, but said the attack happened at 3rd and Harrison streets about 11:40 p.m., about 90 minutes after the conclusion of the game in which the Giants beat the Dodgers, 6-4.
It could not immediately be confirmed whether Denver was wearing Dodger colors, or if others in the fight were wearing Giants gear.
Police declined to comment on a possible motive for the fight.
Three suspects have been detained, said San Francisco police Sgt. Danielle Newman. Denver was rushed to San Francisco General Hospital, where he was pronounced dead.
Detectives are interviewing witnesses as the investigation continues, Newman said. One of the suspects had blood on his shirt, according to KGO-TV.
The Dodgers and Giants have a rivalry going back generations. In 2011, it turned violent when Giants fan Bryan Stow was severely beaten in the parking lot of Dodger Stadium. Two suspects are in custody, charged with the beating.
Stow suffered brain damage and is still recovering.