Melbourne - Patrick Reed's caddie Kessler Karain on Saturday shoved a fan at the Presidents Cup as tensions boiled over after endless barracking of the player by spectators.
Reed, part of Tiger Woods' US team at Royal Melbourne, was docked two strokes for improving his lie in sand in the Bahamas last week, causing International team opponent Cameron Smith of Australia to brand him a cheat.
The row spilled into the biennial match play event with sections of the crowd taunting Reed over the incident he has insisted was unintentional.
Golf Channel personality Steve Sands said the altercation took place after Reed and Webb Simpson were thumped 5 and 3 in the morning fourballs by Taiwan's CT Pan and Japan's Hideki Matsuyama.
"There was a little bit of an altercation earlier today after the morning matches with Patrick Reed and Webb Simpson," he said on air.
ESPN reported that Karain, the brother of Reed's wife, punched the fan, but in a statement to the broadcaster he only admitted shoving him.
Karain said he lost his temper after a fan swore at Reed.
"As a caddy one of your jobs is to protect your player. And unlike several other sports, in golf fans can get pretty close to athletes," he said.
"We have been known for having fun with some good banter, but after hearing several fans in Australia for three days some had taken it too far, I had enough. And this gentleman was one of them.
"I got off the cart and shoved him, said a couple things, probably a few expletives. Security came and I got back in (the) cart and left. I don't think there's one caddy I know that could blame me."
Presidents Cup organisers were not immediately available for comment.
Last week in the Bahamas Reed's practice swings had twice moved sand from behind his ball in a waste bunker, but he insisted he had not deliberately improved his lie, despite being penalised.
After calling him a cheat, Smith admitted earlier this week: "I think our friendship, I guess, is not quite there anymore."