A cheating feud involving world champion Magnus Carlsen and a 19-year-old prodigy is rocking the chess world

• World champion Grandmaster Magnus Carlsen withdrew from a recent chess tournament after losing to 19-year-old Hans Niemann, then seemingly implied Niemann cheated.
• In a rematch at a different tournament on Monday, Carlsen exited the game after making just one move, shocking the chess world.

The chess world has been rocked by a scandal between world champion Magnus Carlsen and Hans Niemann, a 19-year-old American up-and-comer.

On Monday, Carlsen, the world No. 1 and considered one of the greatest chess players of all time, quit after making just one move against Niemann during an online match at the Julius Baer Generation Cup. Carlsen turned off his camera and left.

Carlsen's default comes weeks after Niemann defeated Carlsen at the Sinquefield Cup in St. Louis, Missouri, in a stunning upset.

After that loss at Sinquefield, Carlsen took to Twitter to announce he had withdrawn from the tournament. He also linked to a YouTube video of Roma manager Jose Mourinho saying in a press conference, "If I speak, I am in big trouble. And I don't want to be in big trouble."

Many took Carlsen's tweet to imply that Niemann had cheated during their match, and it set off a flurry of wild, unsubstantiated rumors about the use of sex toys to wirelessly tip off moves.

Carlsen's default on Monday took it further, showing the Norwegian Grandmaster essentially refusing to play the American prodigy.

"It's a giant mess," Maurice Ashley, the first Black grandmaster in history and a chess analyst, told Insider.

Carlsen has refused to speak publicly on his defeat to Niemann, his tweet, or Monday's shocking default.

Meanwhile, the chess community has been abuzz about the potential that Niemann cheated.

While Niemann has denied cheating at the Sinquefield Cup, he did admit to cheating twice online in the past — once at 12 years old and once at 16.

"I cheated on random games on Chess.com," Niemann said. "I was confronted. I confessed. And this is the single biggest mistake of my life. And I am completely ashamed. I am telling the world because I don't want misrepresentations, and I don't want rumors. I have never cheated in an over-the-board game. And other than when I was 12 years old I have never cheated in a tournament with prize money."

Ashley said he believes most chess players would take Niemann's word.

"I think there's some people who just are far more critical of that and say, 'Once a cheater, always a cheater,'" Ashley said. "I think most players, as evidenced by the fact that they're continuing to play him at this event ... I think most players say what's past is past."

Proving cheating during over-the-board matches can be difficult.

To cheat during an over-the-board match, a player would have be receiving secret electronic communication from someone else watching the match, who is plugging the data into AI programs that can determine the best move to make.

"The reality is, any basic computer engine plays better than every human being," Ashley said, adding: "If you can somehow communicate that to the player in the room — then I'm gonna beat Magnus. Anybody's gonna beat Magnus."

However, so far, there is no proof that Niemann cheated.

There are statisticians who analyze chess performances for outliers: Are players suddenly playing in a different way? Are they making significantly different moves than they typically make?

Kenneth Regan, a University of Buffalo faculty member who is an expert in chess and identifying cheaters, even said during Chess24's broadcast of the Julius Baer Generation Cup that he didn't see anything in Niemann's play at the Sinquefield Cup to suggest he cheated.

"Niemann played well. But not too well," Regan said.

Ashley agreed.

"It was a good game. They both made mistakes," he said. "Hans played well; Magnus played worse. It wasn't Magnus' finest moment. It looked like maybe he had a certain feeling going on in him that didn't make him play up to his top level."

In the meantime, the chess community is being left in the dark, wondering what's on the mind of the best player in the game.

"Has anybody showed any data that [Niemann is cheating] now? That he's done so in the last couple of years? I haven't seen any," Ashley said.

"I think the whole world is waiting for that as well as a statement from Magnus about why it is that he's treating Hans differently from everybody else."

Ashley said it's a poor look for the game.

"It's already hurt the world of chess," he said. "Certainly, this is not what we want our game to be known for."