Filed today, Niemann v. Carlsen (E.D. Mo.). I can’t opine on the facts, but I was particularly interested in one of the many claims in the lawsuit:

By insisting that the Sinquefield Cup impose enhanced anti-cheating measures after his loss to Niemann, resigning from the tournament immediately thereafter, and then referencing a famous video of a soccer coach refraining from publicly accusing referees of misconduct, Carlsen conveyed a clear and unmistakable message to the public: that  Niemann only beat Carlsen because Niemann cheated….

As Carlsen intended, the chess world and the public at large received Carlsen’s defamatory message loud and clear. On September 6, 2022, worldchess.com posted an article titled “Did Hans Niemann Actually Cheat? All the Info So Far,” which stated

Yesterday, Magnus Carlsen withdrew from the Sinquefield Cup 2022 after his loss to Hans Niemann in Round 3. Multiple tweets, streams, comments, and security checks later, the accusation of Niemann cheating is pretty obvious!

[Further examples omitted.]

Other claims involve more express statements as well. Thanks to Paul Alan Levy for the pointer.