The debate started last year when Alex Popov, 38, sued Patrick Hayashi, 37, after Bonds homered on Oct. 7, 2001 to finish the season with 73 home runs - three more than Mark McGwire hit during his record-setting 1998 season.
Popov claims he caught the ball but then lost it when frenzied fans at Pacific Bell Park pounced on him. Hayashi came up with the ball, which collectors say could fetch at least $1 million.
"This is about America's pastime and the dream of catching a ball," Martin Triano, Popov's lawyer, said Thursday during opening statements in San Francisco Superior Court. "His dream turned into a nightmare."
Triano said Popov's dream was ruined when he was knocked over by several San Francisco Giants fans, including Hayashi.
Hayashi's lawyer, Michael Lee, said his client never attacked anyone, and claimed that scrambling over baseballs is just part of the game's "fan culture," which states that a home run ball is fair game until someone has complete control of it.
"When Hayashi reached out and grasped the loose home run ball ... it was entirely fair game," Lee said. "Now Alex Popov wants to change the rules. He now criticizes the fan culture that he was once a part of."
Popov had a different take.
"I got mugged," Popov said outside court. "I brought a glove, not a bat."
Kathryn Sorensen, who saw the scuffle, testified that Popov caught the ball, didn't lose it, and was attacked. She said Hayashi was trying to get under Popov's body to get the ball. She also testified she saw Hayashi bite a young man's leg to get him out of the way.
Both sides said they plan to rely on videotaped footage of the ball flying into the stands, and the scene that followed.
Opening arguments in the case were originally scheduled for Wednesday, but Judge Kevin McCarthy delayed them, urging the men to try and settle their differences. They couldn't.
The trial, which resumes Friday, is being heard without a jury and is expected to last three weeks. Also testifying for Popov will be three law professors who specialize in property law. Hayashi's defense includes a major league umpire.
McGwire's then-record No. 70 sold for $2.7 million in 1998. Bonds' 73rd remains in a safe-deposit box.
While the fight over No. 73 continued, four men who landed in court over ownership of Bonds' career 600th home run resolved their dispute out of court Wednesday.
Three friends had sued Jay Arsenault, the man who pocketed the ball Aug. 9 at Pac Bell Park, claiming he had promised to split its value if he should happen to catch it. He made the promise in exchange for tickets to the game.
Initially, after Arsenault ended up with it, he eluded his friends. But on Wednesday, his lawyer said Arsenault was "totally overwhelmed by the situation" and had agreed to sell the ball and split the proceeds.
Solano County Judge William Harrison agreed to the deal, which pre-empted a trial.
"This is better for both sides," said Eric Bergen, one of the men who gave Arsenault his ticket. "This is what we wanted from the beginning."
By Angela Watercutter