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 or pocket. At any time, instead of making a move with a piece on the board, a player can drop a piece from their reserve 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 players' 1st or 8th .
- Promoted but captured pawns are dropped as pawns.
Unlike shogi, having two or more pawns on a file, and 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, P@d5 means "pawn 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 chess programs like Xboard/Winboard, Stockfish, and others. The reserve is given in square brackets following the board position.
r2qk3/pp2bqR1/2p5/8/3Pn3/3BPpB1/PPPp1PPP/RK1R4[PNNNbpp] b - - 89 45
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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- ""IM opperwezen vs LM JannLee in T6Q3tMva : Analysis board • lichess.org"". Lichess. Archived from the original on 2018-05-26. Retrieved 2018-05-26.
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- "Chessgi". ChessVariants.org. 2001-03-20. Archived from the original on 2014-03-27. Retrieved 2014-04-17.