As with all games over a certain age, chess has had a number of anecdotes associated with it, some relating to games that have got out of hand and have resulted in the murder of one of the players.
The reliability of most of the anecdotes is dubious, although some do appear to based on some form of factual event.
Possibly the anecdote with most supporting evidence is given in the book Chess or the King's game (1616) by Augustus, Duke of Lьneburg, who claimed to have obtained it from an old Bavarian Chronicle, then in the library of Marcus Welsor but now lost. The anecdote states that Okarius (also spelt Okar or Otkar), the prince of Bavaria, had a son of great promise residing at the Court of King Pepin. One day Pepin's son was playing at chess with the young Prince of Bavaria, and became so enraged at repeatedly losing that he hit the latter on the temple with one of his rooks and killed him on the spot. This anecdote is repeated in another Bavarian Chronicle, and in a work by Metellus of Tegernsee about Saint Guirin and other documents refer to his death while at Pepin's court.
King Canute, best known for his failed attempts to halt the incoming tide, is said by some to have had Earl Ulf killed after a disagreement about a chess game. By one account, the king made an illegal move that angered the earl, who knocked over the board and stormed off, after which the king sent someone to kill him.