ATLANTA -- Right-hander Randy Messenger's bad temper, not bad luck, caused the fracture in his left hand that has put him on the disabled list.

Messenger confessed Thursday that he punched a plastic equipment cart out of frustration Tuesday after yielding Chipper Jones' ninth-inning RBI double that handed the Giants a 5-4 loss. Messenger said that his hand hurt worse after playing catch Wednesday, prompting the X-rays that showed he had broken the base of his fifth metacarpal.

"Everyone's always been harping on me to stop punching stuff with your right hand. I listen to them, and see what happens," said Messenger, who was said to have been hit by a line drive during batting practice Wednesday.

Figuring that the real source of his injury ultimately would surface, Messenger said that he decided to tell the whole story.

"Why not tell the truth? I'm an honest person. It's going to get out eventually," said Messenger, who was replaced by left-hander Patrick Misch on the active roster. "I wanted to clear the table and let everybody know what really happened."

Trainer Dave Groeschner estimated that Messenger will be sidelined for four to six weeks, though that could change after the right-hander undergoes a magnetic resonance imaging examination and visits hand specialist Dr. Gordon Brody on Tuesday.

Since the injury is to Messenger's non-throwing hand, he'll be able to keep his pitching arm in shape while somebody catches return throws for him.

Now pitching: Lance Niekro, formerly known as the Giants' first baseman, warmed up in the bullpen for Triple-A Fresno and intends to give pitching a try -- following the example of his late father, Joe, and Hall of Fame uncle, Phil.

Like his forebears, Niekro has developed a knuckleball which he believes he can rely on.

"I have nothing to lose," Niekro told The Fresno Bee. "I'm going to go out there and you never know; it could be a turning point or something. ... I'm just having fun."

Said Fresno manager Dan Rohn, "He's got a good knuckleball. We'll see if we can get something out of it."

A day for Bonds: A public celebration honoring Barry Bonds' ascent atop the all-time home run list will be held on Friday, Aug. 24, beginning at noon PT at San Francisco's Justin Herman Plaza.

San Francisco Mayor Gavin Newsom will host the event, which will be emceed by Giants public-address announcer Renel Brooks-Moon. Bonds' former and current teammates, Giants executives and broadcasters, and various celebrities also are expected to attend.

Due back: Manager Bruce Bochy affirmed that infielder Rich Aurilia will be activated from the 15-day disabled list before Friday's game and will start at second base, giving Ray Durham a rest. The Giants likely will shrink their 13-man pitching staff to 12 to clear a roster spot for Aurilia, with Scott Atchison appearing to be the most vulnerable candidate for demotion.

Rough trip: Somewhat remarkably, Misch hasn't pitched since he started against Washington on Aug. 9, immediately before the Giants optioned him back to Triple-A to accommodate Russ Ortiz's return from the disabled list. He was supposed to start Tuesday against Tacoma, but the game was postponed when the Rainiers' equipment never arrived in Fresno due to a transport snafu.

"I couldn't believe it," Misch said.

Misch's start was moved to Wednesday, but he was informed of his recall only slightly more than an hour before the game.

"They said, 'Pack up,'" said Misch, who flew overnight from Fresno to Atlanta through Las Vegas. "I did some laundry as fast as I could. It's all good."

Kind words: Although Ortiz's pitching line Wednesday night was somewhat ordinary (five-plus innings, three hits, four runs, five walks and four strikeouts), he impressed Atlanta manager Bobby Cox.

"He's starting to come around and throw the ball much better like he used to," said Cox, who managed Ortiz in 2003-04. "He had a nice cutter going and a changeup."

Coming up: The Giants open a four-game series Friday against the Florida Marlins at Miami's Dolphin Stadium. San Francisco's Barry Zito and Florida's Scott Olsen will oppose each other in a matchup of left-handers.