Inchess, across-check (orcounter-check) is atactic in which acheck is played in response to a check, especially when the original check is blocked by apiece that itself either delivers check or reveals adiscovered check from another piece. Sometimes the term is extended to cover cases in which theking moves out of check and reveals adiscovered check from another piece (this is also known as aroyal check); it does not generally apply to cases where the original checking piece is captured.
The cross-check is an essential tactic in winning someendgames such as those with twoqueens versus one, or aqueen and pawn versus a queen. In these cases, the defense usually tries for aperpetual check and sometimes the stronger side can stop it only by a cross-check.
A cross-check occurs from time to time in games. It is an essentialtactic in winningendgames such as twoqueens versus one queen, or queen andpawn versus queen, where it is used to stop a series of checks from the opponent and force theexchange of queens. It is also used in somechess problems.
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Cross-checks are rare in actual play, though they do occur, and in someendgames, particularlyqueen endgames, they are very important. The position shown to the right is the final position in the famous queen endgame from the game[1] betweenMikhail Botvinnik andNikolay Minev, Amsterdam Olympiad, 1954. In the position shown, after91. Kc5!!, Blackresigned because the promising looking checks 91...Qc7+, 91...Qg1+, 91...Qf2+ and 91...Qc2+ are answered by the cross-checks 92.Qc6+, 92.Qd4+, 92.Qd4+ and 92.Qc4+ respectively, forcing an exchange of queens in all cases, which will result in thepromotion of thepawn and winning the game by a basiccheckmate. This is an important theme in queen endgames: the weaker side often gives a series of checks, and it is frequently important for them to avoid simplifying cross-checks such as these in reply (Burgess 2000:102–3, 458–59), (Golombek 1977). If the black queen attacks the pawn instead of checking it does no good since the promotion square of the pawn is protected by its queen. Note too that if Black instead merely allows the pawn's promotion, another cross-check may be necessary to win, as in the next section.
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In the position on the left from Botvinnik–Ravinsky,[2] Black resigned. With best play according to theendgame tablebase, 126...Kb3 127.Qf7+ Ka4 128.g8=Q Qg4+ 129.Kh6 Qh4+ 130.Kg7 Qg3+ 131.Kf8 Qd6+ 132.Qe7 Qh6+ 133.Qgg7 Qf4+ 134.Qgf7 Qb8+ and the position on the right is reached. Then the cross-check 135.Qee8+ (or Qfe8+)forks the king and queen, forces an exchange, and wins the game.
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Cross-checks are relatively infrequent in actual play, but are popular inchess problems since they make for a relatively unobvious solution. In the problem shown to the right, White is to move and mate in two moves against any defence. It is byG.F. Anderson and was first published inIl Secolo in 1919. Thekey 1.Kd6, threatening 2.Qb7#, gives the black king twoflight squares, and two of the variations exploit these: 1...Kb6 2.Bc2# and 1...Kb4 2.Kxc6#. The other two defences exploit the fact that the key exposes the white king to checks, and are answered by cross-checks: 1...Rg6+ 2.Be6# and 1...Rd3+ 2.Bd5#.
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The problem to the right, also by G. F. Anderson (first published inThe Observer in 1961) and also a mate in two, features no fewer than five cross-checks. The key is 1.Qb6 (threat: 2.Ne4#), with the following variations:
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