Police are looking for the person or persons who attacked a father of three, apparently unprovoked, after a Anaheim Angels playoff game as he walked to his car with a family member.

The victim, a 43-year-old US Marine veteran from Huntington Beach, California, was knocked out cold Friday night and then beaten repeatedly. Authorities did not release his name.

Witnesses said that the attack appeared unprovoked and that both victim and attacker were wearing Angels gear.

"The guy ran up on him from behind," a witness named Sandra told ABC News affiliate KABC-7 in Los Angeles. "No shouting, nothing. It was just really quick, 'boom, boom, boom.' … He got him really good and then he ran off."

The victim remained hospitalized. The attack ran off with two others, according to KABC-TV.

It wasn't the only sickening and brutal fan-on-fan attack to mar a sporting event this weekend.

Police reportedly used surveillance video to track down and arrest two suspects who allegedly attacked two fans in a restroom at a San Francisco 49ers game Sunday.

YouTube is filled with examples of fan violence, often fueled by drunken spectators at baseball and football games. In some stadiums, including Seattle's, authorities have started posing as undercover fans to deter the violence.

"What we've found is, when people don't know where the police are, they're more likely to be on their best behavior," said Sean Whitcomb of the Seattle Police Department.

In a case that made headlines three years ago - and was a wakeup call to authorities and stadium officials - Bryan Stow, a father of two and San Francisco Giants fan, was brutally beaten outside the Los Angeles Dodgers' stadium.

He suffered a fractured skull and is disabled. His attackers received prison time.