SAN FRANCISCO >> It just started as words between two groups of fans of bitter baseball rivals.

“The back and forth, ‘Go Dodgers!’ ‘Go Giants!'” San Francisco Police Chief Greg Suhr said Thursday. “And it deteriorated from there.”

The verbal sparring Wednesday night turned physical and a man, Jonathan Denver, was fatally stabbed hours after the Los Angeles Dodgers lost to the Giants in San Francisco. Denver’s father, Robert Preece, worked security on game days at Dodger Stadium, the team said.

“There is no rational explanation for this senseless act,” the Dodgers said in a statement. “The pain that this has caused his family and friends is unimaginable.”

Meanwhile, the father of suspect Michael Montgomery, accused of stabbing Denver to death, said his son told him it was done in self-defense.

Police say Denver, 24, was with his father, older brother and two other people a few blocks from the Giants’ stadium after leaving the ballpark in the eighth inning of the Giants 6-4 victory when their group exchanged words with some Giants fans. The Giants fans didn’t attend the game and had left a nightclub.

San Francisco police said Michael Montgomery, 21, of Lodi, was arrested on suspicion of homicide. Suhr said Montgomery made some “incriminating statements” while in custody that led to his arrest.

Another person, whose name was not released, was also taken into custody. Police said they were still looking for two more suspects.

But Montgomery’s father said late Thursday that his son was jumped during the fight, and he stabbed Denver in self-defense.

Marty Montgomery told the Lodi News-Sentinel that his son said by phone that Denver, who was wearing Dodgers apparel, yelled, “Giants suck,” at Montgomery’s friend, who was wearing a Giants hat, when Denver and others hit his son and their friends without warning.

Marty Montgomery said that during the fight, Denver hit his son over the head with a chair, and in self-defense, his son, Michael, stabbed Denver.

“It was a self-defense deal,” Marty Montgomery said. “(Michael) got jumped. (Denver and friends) started swinging chairs and he stabbed (Denver). (Denver) mouthed off about the San Francisco hat. It wasn’t even (Michael’s) hat.”

The father said he had been trying to reach his son on Thursday when his son called him and told him about the fight.

“He’s freaking out,” Marty Montgomery said. “He’s like, ‘I saw him die in his dad’s arms.'”

Denver was born in Los Angeles County but was living in Fort Bragg, about 170 miles north of San Francisco, his friend Matt Gomes said late Thursday. “He was an amazing guy who made everybody happy and made them laugh. He was there for everybody,” Gomes said.

Denver apparently was trying to help a buddy who was getting beat up during the fight, Gomes said. “He was defending his friend,” Gomes said. “And then he got stabbed and died.”

Gomes said he doesn’t believe Denver, his family and friends started the fight.

Janet Alvarado, Denver’s aunt, told KNBC-TV in Los Angeles that Jonathan Denver was a “gentle, sweet boy.” Speaking from her home in Covina, she called his death senseless and said she had no idea how it happened.

“I wish I could tell you how this happened, why this happened. I have no clue why anyone would do this to any family,” she said.

Wednesday’s fatal stabbing was the second violent confrontation between Dodgers and Giants fans in the past several years to end in death or serious injury. Bryan Stow, a Northern California paramedic and Giants fan, suffered a traumatic brain injury after two men dressed in Dodgers gear attacked him following the teams’ March 31, 2011, game in Los Angeles. They are awaiting trial on charges in the beating, which sparked outrage and brought stadium security changes around the state and country.

Stow’s family said in a statement Thursday that they were “horrified and deeply saddened” by Wednesday’s violence. “Our thoughts and prayers go out to the family.”

Denver, who just started a job as a plumbing apprentice, did have two recent brushes with the law in Mendocino County, according to KGO-TV. He was arrested on suspicion of driving under the influence in July, and for public intoxication at the county fair this month.

Police said they didn’t know if alcohol was a factor in Wednesday’s stabbing.

The teams, which moved west from New York in the 1950s, have long been rivals and fans’ emotions run high when the teams play in both cities.

The Giants won the World Series last year and in 2010, but will miss the playoffs this season. The Dodgers, on the other hand, were in last place just two months ago, but clinched the division last week.

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Contributing to this report were Associated Press writers Lisa Leff, Jason Dearen and Haven Daley, and Sports Writer Janie McCauley in San Francisco; AP Sports Writer Beth Harris in Los Angeles; and researcher Rhonda Shafner in New York.