LA JOLLA ? The US PGA Tour was embroiled on controversy Friday as Scott McCarron accused world number two Phil Mickelson of "cheating" for making use of a loophole in new rules governing grooves in clubs.

Mickelson is one of several players at this week's tournament at Torrey Pines using a Ping-Eye 2 wedge, manufactured two decades ago with square grooves.

The square grooves are now banned on the PGA Tour because of a new US Golf Association regulation that club faces have V-shaped grooves.

However, the square-groove Ping wedges remain legal because of a lawsuit that Ping filed against the USGA that was settled in 1990. The outcome of that action was that any Ping-Eye 2 manufactured before April 1, 1990, is approved for play.

"It's cheating, and I'm appalled Phil has put it in play," McCarron told the San Francisco Chronicle in a story published on Friday. McCarron said Mickelson's use of the wedges was against the spirit of the new rules.

While a "cheat" label is abhorrent in golf, a game that prides itself on honesty and self-policing, Mickelson refused enter a debate with McCarron.

Instead Mickelson criticized the rule itself.

"It's a terrible rule. To change something that has this kind of loophole is nuts," Mickelson said. "But it's not up to me or any other player to interpret what the rule is or the spirit of the rule. I understand black and white. And I think that myself or any other player is allowed to play those clubs because they're approved ?end of story."

Square grooves can provide more spin to the ball than V-shaped grooves. The ban is meant to put a greater premium on accuracy off the tee.

Although it isn't clear whether clubs manufactured 20 years ago even produce the same spin as current clubs with V-grooves, Australian Robert Allenby said using old clubs was unfair if only because not all players have access to them.

"I think 'cheating' is not the right word," Allenby said. "But it's definitely an advantage. There's only a certain amount of people that can find them, and I just think it's not right if you're using them."

Japan's Ryuji Imada, who shared the second-round lead at the Farmers Insurance Open on Friday night, said using the Ping wedge couldn't be called cheating, but he thought the loophole in the rule was unfair.

"The rules are the rules, and if it's allowed by the rules of golf, sure, you can use it," Imada said. "But I don't agree with it. If everybody else has to play the V-grooves, I think everyone should have to play the conforming grooves."