US chess grandmaster Hans Niemann is suing rival player Magnus Carlsen for at least $100m after the Norwegian world champion accused him of cheating.
In the latest move in a scandal that has rocked the chess world, Niemann is also suing website Chess.com, which published a report saying he likely cheated in more than 100 online games.
Niemann says the defendants colluded to destroy his reputation and livelihood.
Lawyers for Chess.com said there was “no merit” to Niemann’s allegations.
In his filing, Niemann, 19, accuses Carlsen of launching a smear campaign against him in collaboration with Carlsen’s online chess company Play Magnus, and Chess.com, which has agreed to buy Play Magnus.
He is seeking compensation “to recover from the devastating damages that defendants have inflicted upon his reputation, career, and life by egregiously defaming him and unlawfully colluding to blacklist him from the profession to which he has dedicated his life,” the lawsuit said.
Lawyers for Chess.com dismissed the allegations, and said the company “looks forward to setting the record straight on behalf of its team and all honest chess players.”
Niemann is also suing grandmaster Hikaru Nakamura for repeating the accusations while streaming video content on Chess.com. While streaming, Nakamura said he had no comment.
Carlsen is considered by many to be the greatest chess player of all time, but lost to Niemann in an in-person game in September.
The 31-year-old accused Niemann of cheating, and suggested his rise to prominence in the chess world has been too rapid to be believable. But Niemann has said Carlsen was just unable to cope with defeat, and wanted to ruin the teenage player’s reputation and ensure Niemann would not beat him again.
Neither Carlsen nor Chess.com produced concrete evidence for their cheating accusations. In a 72-page investigation published on the site, Chess.com concluded that Niemann likely cheated in more than 100 online games, including some for prize money.
Its analysis compared his moves to those suggested by computers – which are better than human players – and the probability of his results, among other factors.
Niemann had previously admitted to cheating in informal games on the site when he was 12 and 16, but said he had never done so in competitive games. Following the accusations, Niemann was banned from playing on Chess.com and from in-person tournaments it sponsors.
Niemann’s lawsuit suggested that the move was made under pressure from Carlsen, whose Play Magnus company is being bought for $83m (£74m) by Chess.com. “Carlsen, having solidified his position as the ‘King of Chess,’ believes that when it comes to chess, he can do whatever he wants and get away with it,” the lawsuit said.