In chess, a blunder is a very bad move. It is usually caused by some tactical oversight, whether from time trouble, overconfidence or carelessness. While a blunder may seem like a stroke of luck for the opposing player, some chess players give their opponent plenty of opportunities to blunder.
What qualifies as a "blunder" rather than a normal mistake is somewhat subjective. A weak move from a novice player might be explained by the player's lack of skill, while the same move from a master might be called a blunder. In chess annotation, blunders are typically marked with a double question mark, "??", after the move.
Especially among amateur and novice players, blunders often occur because of a faulty thought process where they do not consider the opponent's forcing moves. In particular, checks, captures, and threats need to be considered at each move. Neglecting these possibilities leaves a player vulnerable to simple tactical errors.
One technique formerly recommended to avoid blunders was to write down the planned move on the scoresheet, then take one last look before making it. This practice was not uncommon even at the grandmaster level. However, in 2005 the International Chess Federation (FIDE) banned it, instead requiring that the move be made before being written down. The US Chess Federation also implemented this rule, effective as of January 1, 2007 (a change to rule 15A), although it is not universally enforced.
Strong players, even grandmasters, occasionally make elementary blunders.
This position is from game 23 of the 1892 World Championship in Havana, Cuba. Chigorin is a piece up (Steinitz lost a knight for a pawn earlier in the game), but his bishop is forced to stay on d6 to protect both the rook on e7 and the pawn on h2. If he won, Chigorin would have tied the match and sent it to a tiebreaker game. After 31...Rcd2, he played 32.Bb4??. Steinitz replied 32...Rxh2+ and Chigorin immediately resigned (in light of 33.Kg1 Rdg2#), losing the match.
The position in the diagram here arose in the 1956 Candidates Tournament in Amsterdam. Petrosian, playing White, enjoys a clear advantage with strong knights, active rooks and plenty of mobility while Black's position is congested and he is hardly able to move. In fact, Bronstein (playing Black) has for the last seven moves been making only apparently aimless knight moves, Nc6–d4–c6–d4, and now has played ...Nd4–f5, threatening White's queen, while White has been slowly strengthening his position. White can now easily preserve the positional advantage by a move like 36.Qc7, but overlooking that the queen was en prise, he played 36.Ng5?? and resigned after 36...Nxd6.
This game between Miguel Najdorf and Bobby Fischer from the 1966 Piatigorsky Cup is an example where a player in a bad position breaks under the pressure. According to Mednis, Fischer's decisive error came earlier in the game and here the black pawn on f4 is about to fall. Fischer played the blunder 30...Nd6?? cutting the game short. After Najdorf played 31. Nxd6, Fischer resigned because he realized after Najdorf's response that 31...Qxd6 32.Nxb7 wins a piece because 32...Rxb7 33.Qc8+ is a fork which wins the rook on b7, so White wins at least a minor piece.
Najdorf commented on Black's 29...Rb8: "There is no satisfactory defense. If 29... Ba8 then 30. Nb6 or 30. Qf5 would win. ... I had to win minor material (the pawn at f4) but this [30... Nd6?] decides immediately. Fischer, demoralized because of his inferior position, did not notice the simple point."
This position is from Game 17 of the 1978 World Championship between Viktor Korchnoi, the challenger, and the World Champion, Anatoly Karpov. Karpov, playing Black, is hoping for a back rank mate with his rook with the possible move 39...Rc1#. However, Korchnoi could have prevented this by moving his g-pawn (but not the h-pawn because 39.h3 or h4 leads to 39...Rc1+ 40.Kh2 Nf1+ 41.Kg1 Nfg3+ 42.Kh2 Rh1#), providing an escape square for his king. Korchnoi did not notice Karpov's mate plan with his knights however, and played 39. Ra1??. It allowed a nice finish for Karpov, 39...Nf3+!, and Korchnoi resigned the game. Otherwise, Black would checkmate after 40. gxf3 Rg6+ 41. Kh1 Nf2# or 40.Kh1 Nf2#. Karpov went on to win the match and later beat Korchnoi again in 1981 in the "Massacre in Merano".
In this example, from a tournament in Biel in 1987, the game did not result in a loss for the blunderer, but led to an embarrassing draw for the British GM Chandler. Susan Polgar has just played the wily trap 53...Ng8–h6!?, hoping to turn the game around. Chandler realizes that after 54.gxh6+ Kxh6 he will be left with the considerable material advantage of a rook pawn and bishop against a bare king. However, since the bishop is unable to control the promotion square h8, Black will draw if she is able to get her king to control h8 due to the wrong rook pawn fortress. But Chandler calculates further, and realizes that it is he who will win control over the h8 square after 55.Kf6, and thereby win the game.
Therefore Chandler played 54.gxh6+??, but instead of the expected 54...Kxh6 came 54...Kh8! This is in fact almost the same king, bishop, and rook pawn versus bare king situation as Chandler had calculated that he would avoid, and the small difference that White has two rook pawns rather than one has no effect on the result. Black controls the h8 square and cannot be chased or squeezed away from it, and so White cannot promote his pawn. After 55.Bd5 Kh7 56.Kf7 Kh8 the players agreed to a draw.
Chandler had numerous moves which would have maintained his winning position, the fastest according to the Shredder tablebase are 54.h4 and 54.Bf5.
This example, from a game played in Linares in 2002, is one of the very rare circumstances where a grandmaster makes the worst move possible, the only one allowing checkmate on the next move. In this queen endgame, White has some advantage after 69.fxg6+ fxg6 70.Kf4 due to Black's weak pawn on c6. However, Beliavsky playing White played 69.Kf4??, overlooking the response 69...Qb8#. According to Johannessen, it took a few moments for both players to realize that it was checkmate, and Beliavsky was a good sport over this mishap.
In November 2006, reigning World Chess Champion Vladimir Kramnik competed in the World Chess Challenge: Man vs. Machine, a six-game match against the chess computer Deep Fritz in Bonn, Germany. After the first game had ended in a draw, Kramnik, playing Black, was generally considered in a comfortable position in Game 2, and he thought so himself apparently, as he refused a draw by avoiding a potential threefold repetition on 29...Qa7. Kramnik's troubles began when he decided to play for a win and pushed his a-pawn, 31...a4. Commentators, including American grandmaster Yasser Seirawan, voiced concerns about Kramnik's intentions and the situation became more uncertain as the game went on with 32.Nxe6 Bxe3+ 33.Kh1 Bxc1 34.Nxf8, turning it into a likely draw. The game could have ended with 34...Kg8 35.Ng6 Bxb2 36.Qd5+ Kh7 37.Nf8+ Kh8 38.Ng6+.
However Kramnik's next move, 34...Qe3?? (a move which was awarded "???" originally by ChessBase on a story covering Kramnik's blunder, and even "??????" by Susan Polgar), came as a big surprise and was described as possibly the "blunder of the century" and perhaps the "biggest blunder ever" by Susan Polgar, as Kramnik overlooked a mate in one. Deep Fritz immediately ended the game with 35.Qh7#, checkmate. Seirawan later called Kramnik's move "a tragedy".
ChessBase described the events as follows, "Kramnik played the move 34...Qe3 calmly, stood up, picked up his cup and was about to leave the stage to go to his rest room. At least one audio commentator also noticed nothing, while Fritz operator Mathias Feist kept glancing from the board to the screen and back, hardly able to believe that he had input the correct move. Fritz was displaying mate in one, and when Mathias executed it on the board Kramnik briefly grasped his forehead, took a seat to sign the score sheet and left for the press conference, which he dutifully attended." During it he stated that he had planned the supposedly winning move 34...Qe3 already when playing 29...Qa7, and had rechecked the line after each subsequent move. After an exchange of queens Black would win easily with his distant pawn; after 35.Qxb4 Qe2 or 35.Ng6+ Kh7 36.Nf8+ Kg8 Black also wins eventually.
Chess journalist Alexander Roshal attempted to explain the blunder by saying that the mating pattern of a queen on h7 protected by a knight on f8 is extremely rare and not contained in a grandmaster's automatic repertoire.
This game was played in May 2008 at the Baku Grand Prix from the FIDE Grand Prix 2008–2010. In round 11, Étienne Bacrot played White against Ernesto Inarkiev. On move 23, he checked the Black king with 23. Qe7+??. Both players calmly wrote down the move. Bacrot then realized that his Queen was under attack by the Black knight, and resigned.
The game between the World's two highest-rated players in the 2012 Grand Slam Master's final in São Paulo and Bilbao (this game was played in São Paulo) featured a double blunder. Carlsen, with White, played the tactical blunder 27.Bf4??, and saw almost immediately that this loses to 27...R8xf4!, in effect winning a piece since taking the rook gives Black a forced mate: 28.gxf4 Nxf4 (threatening Qg2#) 29.Rg1 Qxh2+ 30.Kxh2 Rh3#.
Carlsen waited for Aronian to make his move, and Aronian eventually played the otherwise solid 27...Bc3??, allowing White back into the game. Aronian had seen 27...R8xf4, but playing quickly to avoid time trouble, he thought that White could strike back with 28.gxf4 Nxf4 29.Ra8+ since both 29...Kf7 and 29...Kh7 lose to the knight fork 30.Ng5+. However he had missed that the retreat 29...Bf8! ends White's brief counterattack and leaves White defenseless against the mate threat.
The game was eventually drawn by perpetual check on move 48.
The sixth game of the World Chess Championship 2014 between Magnus Carlsen and Viswanathan Anand also featured a double blunder. Carlsen adopted the space-gaining Maróczy Bind setup against the Kan Variation of the Sicilian Defence, and accepted a set of isolated doubled pawns in return for active play. After an early queen exchange he soon developed a commanding position and appeared to have excellent winning chances. On his 26th move Carlsen played 26.Kd2??, immediately realizing after making the move that 26...Nxe5! (with a discovered attack on the g4-rook) 27.Rxg8 Nxc4+ (zwischenzug) 28.Kd3 Nb2+ 29.Ke2 Rxg8 leads to Black picking up 2 extra pawns and gaining excellent winning chances. Anand, not expecting the blunder, replied with 26...a4?? in less than a minute. He, too, saw the missed tactic immediately after making his move. Carlsen made no further mistakes and converted his advantage into a win.
Sometimes players, including strong grandmasters, resign a position which they are actually winning, not losing. Chess historian Tim Krabbé calls this kind of mistake "the ultimate blunder".
In this "earliest, most famous, and clearest example" of resigning with a winning position, the black bishop on d4 is pinned to the rook on d7, and there are no additional friendly pieces to come to its defense. Seeing no way to save his bishop, Georg Marco resigned, having missed 36... Bg1!, threatening Qxh2# and leaving no way for Ignatz von Popiel, playing white, to save both his queen and rook while staving off checkmate.Mikhail Chigorin v. Wilhelm Steinitz, Havana 1892
Tigran Petrosian v. David Bronstein, Amsterdam 1956
Alexander Beliavsky v. Leif Erlend Johannessen, Linares 2002
Murray Chandler v. Susan Polgar, Biel 1987
Deep Fritz v. Vladimir Kramnik, Bonn 2006 (chessbase.com)
Viktor Korchnoi v. Anatoly Karpov, 1978
Deep Fritz v. Vladimir Kramnik, 2006 (chessgames.com)
Miguel Najdorf v. Bobby Fischer, 1966
Étienne Bacrot v. Ernesto Inarkiev, 2008
Magnus Carlsen v. Levon Aronian, 2012
Ignatz von Popiel v. Georg Marco, 1902