The Ryder Cup descended into chaos after a controversial finish to the final fourballs session, but what led to Team Europe and Team USA being involved in such a heated exchange?
Europe were six points ahead of Zach Johnson's side when the final match of the session reached the 18th green at Marco Simone GC, where Patrick Cantlay - who had been mocked all day for his decision to not wear a cap - holed a long-range birdie to win the point for Team USA.
The closing birdie sparked wild celebrations form the American players around the green, while Cantlay's caddie Joe LaCava was also involved and appeared to annoy Rory McIlroy, initially by encroaching on the Northern Irishman's space as he lined up his own putt and then by waving his cap.
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McIlroy and several European players were involved in a conversation with LaCava after the former world No 1 missed his birdie effort, which would have extended their lead going into the final day, with the arguments continuing to escalate and finishing in the car park.
Shane Lowry had to usher McIlroy away from outside the clubhouse and into a courtesy car, having seen his team-mate also point angrily and shout near Justin Thomas' caddie Jim 'Bones' Mackay, with the unsavoury scenes concluding an extraordinary Saturday in Rome.
The incident quickly went viral on social media and generated interest from across the sporting world, with the argument raising plenty of talking points to answer. Former Ryder Cup captains Sir Nick Faldo, Paul Azinger and Paul McGinley took a closer look at the bust-up…
Why did the atmosphere around the course change?
Paul Azinger: "The crowd had been taunting Cantlay the entire day and you can only take so much. I know in America, the Europeans took a beating at Whistling Straits and they think we should be able to take that too. But after a while, human nature comes out.
"Rory McIlroy is the happy-go-lucky guy, I love and respect him, but he wasn't happy-go-lucky because it's the Ryder Cup, and the intensity is so magnified and real.
"The Europeans have almost turned Seve Ballesteros into a deity, who was one of the most emotional and contentious players in Ryder Cup history, and that's just part of what inspires Europe. Somehow, the Americans have become afraid to have inspiration like that.
"In that situation, the happy-go-lucky Rory would laugh at Joey in his space and not think it to be malicious, but this wasn't happy-go-lucky Rory, this was the most intense Rory you'll ever see, this is revenge Rory."
What did LaCava do wrong?
Sir Nick Faldo: "Joe [LaCava] got in Rory's space, as McIlroy wanted to come around and read, as we usually do from 360 degrees. He is in his space and Rory's asked for him to move, and Joe - from what we see - retaliates verbally, which was wrong.
"If he'd just said, 'sorry mate', and backed off, none of this would've happened. But obviously, there's some animosity there, so he thought, 'sod you, I'm still in here putting up with this crowd'.
"He has another go at Rory, and that's really what's caused the blood pressure to go up. He waves the hat and asks for space, but to chase after him and give him another mouthful after they've already spoken is seriously wrong."
Paul McGinley: "The mistake that Joe made was not waving his hat and having a go at the crowd, he's entitled to do that. It was getting into Rory's space as he was preparing to hole a putt."
Were both parties to blame?
Paul Azinger: I'm not trying to be evasive in any way here, Joe [LaCava] was definitely out of line there, he was in the wrong spot, he just didn't need to be there. He's got no business ever saying anything to another player like that, it's dreadful.
"At the same time, a normal Rory McIlroy is going to say 'get out of there' in a jokey way, but at the Ryder Cup it's just so much more drama. Joe's out of line, but Rory's on edge too.
"McIlroy has had an emotional year, the [PGA] Tour really turned their back on him, they negotiated behind his back while Rory was out there as a front man. And when he got angry in the parking lot, I was saying 'go get him Rory, let it all out baby', because he's got to have this built-in frustration."
Paul McGinley: "It's very difficult playing away from home. I remember being the vice-captain at Medinah and the stick that we got, that Ian Poulter got - and he ended up being the hero - was unbelievable. Poulter took that emotion and channelled that animosity in a very stoic way.
"Saturday afternoon was the first time we saw fight from the American team. If you go back two years ago, we were very soft too, we didn't have a lot of fight about us. One of the things that Luke [Donald] and his team have tried to reinstall is that sense of edge and competitiveness, and I think it just spilled over yesterday.
Should there be an issue with teams arguing?
Paul McGinley: "I don't have a problem with it. I know it looks a bit unsightly, but Luke [Donald] has instilled a passion in this team that we were lacking and it's great to see it means so much to them.
"The emotions are stirred because that's what sport is about, it's about being emotionally invested in something whether you're a player or a supporter. When there's an emotional investment, that's when it's electric, and that's what makes the Ryder Cup so great."
What happened next?
NBC reported that LaCava reached out to McIlroy and European team on Saturday night and then met with McIlroy on Sunday to apologise for the incident, in attempt to clear the air ahead of the final day.
Cantlay was booed as he made his way to the tee for his singles match against Justin Rose on Sunday, with the former FedExCup champion receiving chants of 'Cantlay, where's your cap?' from the packed grandstand.
Several members of the USA team showed solidarity to Cantlay by electing to remove their caps for the pre-match photos ahead of their singles clashes.
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