Crazyhouse (also known as drop chess, mad chess, reinforcement chess and turnabout chess) is a chess variant in which captured enemy pieces can be reintroduced, or dropped, into the game as one's own. It was derived as a two-player, single-board variant of bughouse chess.
Its drop rule is reminiscent of shogi [1] and the games are often compared, though there is no known evidence suggesting that shogi provided direct inspiration for the gameplay of bughouse or crazyhouse.
Though the four-player "bughouse" chess became prominent in western chess circles in the 1960s, the crazyhouse variant did not rise to prominence until the era of 1990s online chess servers, though it may be traced back further to the "Mad Mate" variant made in 1972 by Alex Randolph, a Bohemian-American game designer who moved to Japan and became an amateur dan-level Shogi player.
The rules of chess apply except for the addition of drops, as explained below.
Unlike in shogi, dropping a pawn on a file containing another pawn of the same color and dropping a pawn to deliver checkmate are both permissible. [3]
Crazyhouse's notation system is an extension of the standard algebraic notation. A drop is notated like a standard move, except an at sign is placed immediately before the destination square. For example, N@d5 means "knight is dropped on d5." [2]
There is no standard FEN specification for Crazyhouse. Lichess uses an extended version of FEN, adding a 9th rank as a reserve. Here is an example of Lichess's FEN implementation: [4]
r2qk3/pp2bqR1/2p5/8/3Pn3/3BPpB1/PPPp1PPP/RK1R4/PNNNbpp b - - 89 45
In XBoard/Winboard's notation system, the reserve is given in square brackets following the board position:
r2qk3/pp2bqR1/2p5/8/3Pn3/3BPpB1/PPPp1PPP/RK1R4[PNNNbpp] b - - 89 45
In Chess.com's notation system, the reserve is located after the full-move number.
To keep track of which pieces are promoted, Lichess and XBoard/Winboard use "~" after the letter designation. Chess.com uses the coordinates of the pieces. [5] [ failed verification ]
r2q1r1k/2p1ppb1/p2p2pp/3P1p2/B6B/2N2NPp/1PP2P1K/3Q3q w - - 0 26 NNBRpr h1
GM Larry Kaufman wrote: "[Crazyhouse] is rather fun and interesting, but the games tend to be short, and it is almost certain that White has a forced win, although it would probably be too difficult to prove this and certainly too difficult to memorize all the possible variations." [6]
Crazyhouse has several related variants:
Shogi, also known as Japanese chess, is a strategy board game for two players. It is one of the most popular board games in Japan and is in the same family of games as Western chess, chaturanga, xiangqi, Indian chess, and janggi. Shōgi means general's board game.
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Bughouse chess is a popular chess variant played on two chessboards by four players in teams of two. Normal chess rules apply, except that captured pieces on one board are passed on to the teammate on the other board, who then has the option of putting these pieces on their board.
Minishogi is a modern variant of shogi. The game was invented around 1970 by Shigenobu Kusumoto of Osaka, Japan. The rules are nearly identical to those of standard shogi, with the exception that it is played on a 5x5 board with a reduced number of pieces, and each player's promotion zone consists only of the rank farthest from the player.
A fairy chess piece, variant chess piece, unorthodox chess piece, or heterodox chess piece is a chess piece not used in conventional chess but incorporated into certain chess variants and some chess problems. Compared to conventional pieces, fairy pieces vary mostly in the way they move, but they may also follow special rules for capturing, promotions, etc. Because of the distributed and uncoordinated nature of unorthodox chess development, the same piece can have different names, and different pieces can have the same name in various contexts as it can be noted in the list of fairy chess pieces.
Forsyth–Edwards Notation (FEN) is a standard notation for describing a particular board position of a chess game. The purpose of FEN is to provide all the necessary information to restart a game from a particular position.
The Free Internet Chess Server (FICS) is a volunteer-run Internet chess server. It was organised as a free alternative to the Internet Chess Club (ICC), after that site began charging for membership.
In chess, promotion is the replacement of a pawn with a new piece when the pawn is moved to its last rank. The player replaces the pawn immediately with a queen, rook, bishop, or knight of the same color. The new piece does not have to be a previously captured piece. Promotion is mandatory when moving to the last rank; the pawn cannot remain as a pawn.
Chu shogi is a strategy board game native to Japan. It is similar to modern shogi in its rules and gameplay. Its name means "mid-sized shogi", from a time when there were three sizes of shogi variants that were regularly being played. Chu shogi seems to have been developed in the early 14th century as a derivative of dai shogi. There are earlier references, but it is not clear that they refer to the game as we now know it.
Yari shogi is a modern variant of shogi ; however, it is not Japanese. It was invented in 1981 by Christian Freeling of the Netherlands. This game accentuates shogi’s intrinsically forward range of direction by giving most of the pieces the ability to move any number of free squares orthogonally forward like a shogi lance. The opposite is true of promoted pieces which can move backward with the same power.
Judkins shogi is a modern variant of shogi, however it is not Japanese. Credit for its invention has been given to Paul Judkins of Norwich, UK, prior to April 1998.
Heian shōgi is a predecessor of modern shogi. Some form of the game of Chaturanga, the ancestor of both chess and shogi, reached Japan by the 9th century, if not earlier, but the earliest surviving Japanese description of the rules dates from the early 12th century. Unfortunately, this description does not give enough information to actually play the game, but this has not stopped people from attempting to reconstruct this early form of shogi.
Kyoto shogi is a modern variant of shogi. It was invented by Tamiya Katsuya c. 1976.
Heian dai shogi is an early large board variant of shogi as it was played in the Heian period. The same 12th century document which describes the Heian form of shogi also describes this variant. Unfortunately, this description does not give enough information to actually play the game, but this has not stopped people from attempting to reconstruct this early form of shogi. A fairly complete and playable reconstruction is outlined here.
Dai shogi or Kamakura dai shogi (鎌倉大将棋) is a board game native to Japan. It derived from Heian era shogi, and is similar to standard shogi in its rules and game play. Dai shogi is only one of several large board shogi variants. Its name means large shogi, from a time when there were three sizes of shogi games. Early versions of dai shogi can be traced back to the Kamakura period, from about AD 1230. It was the historical basis for the later, much more popular variant chu shogi, which shrinks the board and removes the weakest pieces.
Cubic chess is a chess variant invented by Vladimír Pribylinec beginning with an early version in 1977. The game substitutes cubes for the chess pieces, where four of the faces of each cube display a different chess piece, the two other faces are blank and are orientated to the players. This provides an efficient means to change a piece's type. Kings and queens have unique cubes containing only their symbol, effectively behaving as normal.
Dragonfly is a chess variant invented by Christian Freeling in 1983. There are no queens, and a captured bishop, knight, or rook becomes the property of the capturer, who may play it as their own on a turn to any open square. The board is 7×7 squares, or alternatively a 61-cell hexagon with two additional pawns per side.
Hostage chess is a chess variant invented by John A. Leslie in 1997. Captured pieces are not eliminated from the game but can reenter active play through drops, similar to shogi. Unlike shogi, the piece a player may drop is one of their own pieces previously captured by the opponent. In exchange, the player returns a previously captured enemy piece which the opponent may drop on a future turn. This is the characteristic feature of the game.
Shogi notation is the set of various abbreviatory notational systems used to describe the piece movements of a shogi game record or the positions of pieces on a shogi board.