SAN FRANCISCO (Map, News) - An act of chivalry may have led to a heated argument outside the gates of AT&T Park and ultimately to the killing of an 18-year-old baseball fan on Friday night.

Anthony Giraudo and a group of friends had left the San Francisco Giants game Friday night and were walking through Seals Plaza when an argument broke out with another group, police spokesman Sgt. Neville Gittens said. The victim’s father, Bob Giraudo, said Giraudo’s friends told police Friday that the argument was over an inappropriate slight directed at a female companion in Giraudo’s group.

Anthony Giraudo was then attacked as he walked away from the argument, stumbled and struck his head on the ground, police said. He died a day later at San Francisco General Hospital. The teenager who allegedly threw the punch is in jail today on suspicion of murder.

“I guess they came from behind and sucker-punched him,” Bob Giraudo said.

The victim’s father said his son was a talented athlete who had graduated last year from Woodside High School and attended Cañada College in Redwood City as a redshirt freshman. He said he took a great deal of pride in his son’s talent.

“It was a tragedy and I lost my best friend,” he said.

Police arrested Taylor Buckley, 18, of San Carlos, that night on an assault charge and was released after making bail. The victim’s death from severe brain trauma at noon Saturday, however, prompted the charges against Buckley to be changed to murder. Buckley surrendered to police Saturday, Gittens said. Buckley and Anthony Giraudo did not know each other, he said.

Family and dozens of friends packed the emergency room at San Francisco General Hospital throughout the weekend as Giraudo was kept on life support so his organs could be donated. Many were in disbelief that a punch could lead to such an extreme result.

“He was the toughest kid on our team and he wasn’t scared of anything,” Woodside High School pitching coach Nick Rewak said. The coach said Giraudo’s pitching skills played a pivotal role in Woodside’s Peninsula Athletic League Ocean Division championship victory last year.

The death comes as a trial about another alleged postgame slaying nears completion. In 2004, Redwood City resident Timothy Griffith was killed in a fight following an AT&T Park game in which Barry Bonds hit his 700th home run.

A spokeswoman for the Giants said that while both incidents were horrible and tragic, violence is relatively rare at the ballpark.

“These things do happen, and all we can do is really try to redouble our efforts,” said Staci Slaughter, vice president of communications for the Giants.

bbegin@examiner.com

Examiner Staff Writer Mike Rosenberg contributed to this report.