Europe's Rory McIlroy asked for a foul-mouthed American fan to be thrown out of the Ryder Cup during his fourball win with Thomas Pieters on Saturday.
The Northern Irishman, 27, said he was verbally abused when he was walking to the eighth tee, stopping to point the offender out to officials at Hazeltine.
"Someone said a few derogatory things I thought were over the line," said McIlroy after winning a third point.
"That particular guy, who is in a small minority, just took it a bit too far."
It is unclear if the man was escorted off the course and McIlroy said he was "unsure if the man had been removed".
Europe, who trail the United States 9½-6½ after the opening two days, need 7½ points from Sunday's 12 singles matches to retain the trophy.
- Day 3 preview: McIlroy faces Reed in opening singles
- Tom Fordyce: Europe need momentum and miracles
- Ryder Cup scores, schedule and teams
- Your all-time Ryder Cup teams
McIlroy and rookie Pieters were the only winners for Europe in the afternoon fourball session as the home side, spurred on by a partisan crowd in Minnesota, won the final three matches.
"It's a tough environment but we expect that," said McIlroy.
"There have been some boundaries crossed. I let it get to me a couple of times which I probably shouldn't have.
"You have to keep your concentration out there and it's been a long day and sometimes emotions run high.
"It fuelled me a lot. The more they shouted, the better we played, so I hope they shout at us all day on Sunday."
Europe team-mate Sergio Garcia, who is playing in his eighth Ryder Cup, said that the atmosphere had "been quite poor". One fan was heard to shout "Sergio, you suck" during the fourballs, leading Tom Lehman, one of the US vice-captains, to tell people to calm down.
The Spaniard, who, alongside German Martin Kaymer, was beaten two and one by Phil Mickelson and Matt Kuchar in the fourballs, told BBC Radio 5 live: "85% of people are great.
"I love playing in America and my girlfriend is American, but the 15% that are really bad makes them look bad, and I feel ashamed for my girlfriend."
Ian Poulter, one of Europe's vice-captains after injury prevented him qualifying, tweeted: "Irrespective of the score the US players are policing the fans as they are embarrassed of their behaviour. Shame some spoiling this."
Captain Darren Clarke tried to play down the issue, saying "people are exuberant and enjoying themselves," before adding, "people just seemed to enjoy themselves a little bit too much at times".
US player Jordan Spieth tried to quieten spectators during the foursomes match involving Garcia, and said: "There were times it would quiet down and you would get a fan or two that would just yell and single people out.
"We wanted to hush them down so they were able to hit under the same conditions we were. I think that's fair.
"We wanted to beat them at their best and we thought it would be fair to make sure we did our part in giving them the opportunity we had when we were hitting shots."