Emotions ran high at the San Diego Open on Friday when Phil Mickelson was accused of cheating by fellow American Scott McCarron and double major winner John Daly said he was quitting the game.
World number two Mickelson was criticised by McCarron for exploiting a loophole in golf's new groove rules by using a 20-year-old Ping wedge and fan-favourite Daly told the Golf Channel he was finished after missing the second-round cut.
McCarron, who also missed the cut at Torrey Pines on Friday, said Mickelson was "taking an unfair advantage of the rules".
In an interview with the Golf Channel, he added: "Golf is a gentleman's game and most of us out here on the PGA Tour don't think it's the right thing to do."
Although McCarron backed off on again using the word 'cheat', he had told Friday's San Francisco Chronicle: "It's cheating and I'm appalled Phil has put it in play.
"All those guys should be ashamed of themselves for doing that. As one of our premier players, (Mickelson) should be one of the guys who steps up and says this is wrong."
As of January 1, new rules relating to club-face grooves were implemented at the top level after research found modern configurations could allow players to generate almost as much spin with irons from the rough as from the fairway.
All clubs, with the exception of drivers and putters, have been affected by the change, which limits groove volume and groove-edge sharpness, effectively replacing U-grooves with V-grooves.
McCarron took exception to the Ping-Eye 2 wedge used by Mickelson, a club with square grooves, which is legal because of a lawsuit won by its manufacturer over the United States Golf Association (USGA) in 1990.
Mickelson agreed with McCarron's overall stance but took exception at how his compatriot had made his point.
"I totally agree with him (McCarron)," Mickelson told reporters after shooting a five-under-par 67 in the second round. "I think it's a ridiculous rule.
"But it's not up to me or any other player to interpret what the interpretation of the rule is or the spirit of the rule. All my clubs are approved for play, and I take that very seriously not to violate any rule.
"I've been talking with Dick Rugge of the USGA and talking to the (PGA Tour) commissioner and explaining behind closed doors how ridiculous all this is. I don't agree with the way he (McCarron) carried on about it, but that's his choice."
Later on Friday, the PGA Tour said in a statement: "We have been aware... the pre-1990 clubs would be allowed and that there was the potential that some players might choose to use them. We will monitor this situation as we move forward."
Shortly before Mickelson completed his round on the North Course, Daly signed for a 71 on the same layout before telling the Golf Channel: "I'm done with golf.
"I just can't do it any more. I'm tired of embarrassing myself. I can't keep taking spots from guys out here playing this bad."
Daly, who has missed his first two PGA Tour cuts of the year, has played on sponsor's exemptions since losing his past champion category after the 2007 season.
He has not won on the US circuit since the 2004 Buick Invitational.