Magnus Carlsen has shockingly withdrawn from the Sinquefield Cup after his loss to Hans Niemann in Round 3. He tweeted just before the start of Round 4 with a video clip of Jose Mourinho commenting, "if I speak I am in big trouble".

The first suggestion anything was up in the Sinquefield Cup was when we learned the broadcast would be delayed by 15 minutes for Round 4, a measure usually applied to prevent cheating.

Before Magnus Carlsen made his announcement the commentators noted that the players were subject to enhanced checks

Then Magnus dropped his bombshell.

The announcement caught both the official broadcast and the players off-guard, with Magnus Carlsen's clock started for his game against Shakhriyar Mamedyarov.

The obvious implication of Carlsen's withdrawal and other changes in St. Louis is that Magnus suspects foul play but is unwilling to make a public accusation. On the previous day he lost a 53-game unbeaten streak against Hans Niemann.

If the decision was based on that game, our chess24 commentary team had doubts. IM Lawrence Trent commented:

GM Rustam Kasimdzhanov agreed:

Hikaru Nakamura, meanwhile, raised questions about Hans Niemann's interview after his win over Magnus — for instance how Hans said he just happened to look at the exact rare line that happened in the game the morning before — and pointed out earlier cheating allegations.

The players in the tournament have also been reacting. Wesley So pointed out that everyone was distracted, while Ian Nepomniachtchi described Hans' win over Magnus as "more than impressive".

Levon Aronian was ready to give young players the benefit of the doubt, pointing out that assuming they can play well and aiming to learn from them is in general the best approach.

Magnus has played less than 50% of his games, so that the games he played will be annulled for the standings, though they still count for rating. In terms of the tournament it's good news for Ian Nepomniachtchi, who lost to Magnus, and bad news for Hans Niemann, who won.

Magnus Carlsen was in the tie for 3rd place on 50%

The impact of this shock news is sure to reverberate around the chess world in the days and potentially years to come.