SAN JOSE — One man was shot and several people were detained after a dispute that erupted among fans watching the 49ers-Raiders game at a downtown restaurant Sunday afternoon.

The victim, who was not identified, was transported with life-threatening wounds to a hospital. He was undergoing surgery Sunday night. San Jose Police responding to a 5:15 p.m. call from people at Britannia Arms on West Santa Clara Street found a man suffering from at least one gunshot wound, Officer Albert Morales said.

According to a source, the victim was a security guard who was trying to break up a dispute outside the bar. However, police would not confirm that.

Sometime afterward, officers detained several adult male suspects around the corner on North Almaden Avenue, in front of SP2 bar and restaurant. Police would not say how many people were detained or release their identities. They were taken to the San Jose police headquarters.

Before the shooting, customers were watching the football game at Britannia Arms, but police did not release any details of any verbal exchanges or altercations. However, the crime “is game-related for sure,” said Sgt. Jaime Jimenez, referring to the 24-13 upset victory by the Raiders over the 49ers.

The attack appears to be an isolated incident, he said. Morales said that officers investigating the shooting were canvassing the area.

If the attack stemmed from the well-known rivalry between the teams, it contrasts with the relative peace at the game, which was played in Oakland. Officials had feared a repeat of the last three Raiders-49ers games, when violent brawling erupted and fans were arrested.

Contact Sharon Noguchi at 408-271-3775. Follow her at Twitter.com/noguchionk12.