Crazyhouse (also known as drop chess, mad chess, reinforcement chess, turnabout chess and schizo-chess) is a chess variant similar to bughouse chess, but with only two players. It effectively incorporates a rule from the game shogi, in which a player can introduce a captured piece back to the chessboard as their own.
|This article uses algebraic notation to describe chess moves.|
All the rules and conventions of standard chess apply, with the addition of drops, as explained below.
- A captured piece reverses color and goes to the capturing player's reserve, pocket or bank. At any time, instead of making a move with a piece on the board, a player can drop a piece from their reserve (a piece in there is considered “held” or “in hand”) onto an empty square on the board. For example, a check that would result in checkmate in standard chess can be answered in Crazyhouse, if the defender can play a legal drop that blocks the check.
- Drops resulting in immediate checkmate are permitted. Unlike in shogi, this includes pawn drops.
- Pawns may not be dropped on the 1st or 8th .
- Pawns that have been promoted and later captured are dropped as pawns. (As in shogi.)
Unlike in shogi, having two or more pawns on a file, as well as checkmating with a dropped pawn, are both permissible.
An extension to the standard chess notation is used to record drops. Drops are notated by the piece type, followed by an @ symbol, then the destination square. For example, N@d5 means "knight is dropped on d5 from reserve".
r2qk3/pp2bqR1/2p5/8/3Pn3/3BPpB1/PPPp1PPP/RK1R4/PNNNbpp b - - 89 45
Lichess simply adds a 0th rank as a reserve. There are more than 8 pieces on the reserve, so the last section may have more than 8 characters.
A different notation is used by Xboard/Winboard. The reserve is given in square brackets following the board position.
r2qk3/pp2bqR1/2p5/8/3Pn3/3BPpB1/PPPp1PPP/RK1R4[PNNNbpp] b - - 89 45
Chess.com uses another notation. The reserve is put after full-move number.
To keep track of which pieces currently on the board are actually promoted pawns, Lichess and Xboard/Winboard use "~" after letter designation. However, Chess.com uses coordinates of promoted pawn to resolve it.[failed verification]
r2q1r1k/2p1ppb1/p2p2pp/3P1p2/B6B/2N2NPp/1PP2P1K/3Q3q w - - 0 26 NNBRpr h1
Minor variations of the rules have resulted in some variants.
- Loop Chess: promoted pawns keep their rank when captured.
- Chessgi (also known as Mad Mate or Neo Chess): promoted pawns keep their rank when captured. Pawns may be dropped on the 1st rank.
- Hostage Chess—a player can drop back into play their own previously captured pieces
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- "Game rules (Loop Chess)". BrainKing. Retrieved 2014-04-17.
- "Chessgi". ChessVariants.org. 2001-03-20. Archived from the original on 2014-03-27. Retrieved 2014-04-17.