Rollerball (chess variant)



Rollerball is a chess variant invented by Jean-Louis Cazaux in 1998. The game was inspired by the 1975 science-fiction movie Rollerball, specifically the futuristic and violent sport (similar to Roller Derby) portrayed in the film.

The board comprises 7×7 squares with the central 3×3 section missing. Pieces generally move clockwise around the board. Each player starts with one king, one bishop, two rooks, and two pawns. Both bishops are light-squared on the initial setup. Dark-squared bishops can only be obtained by pawn promotion.

Game rules
The initial setup is as shown. White moves first. Pieces move and capture the same as their chess counterparts, except where explained differently below.

Objective
There are two ways to win in Rollerball:
 * 1) Checkmating the enemy king.
 * 2) Bringing one's own king to the starting square of the enemy king on the opposite side of the board (but only when having travelled to that side of the board in a clockwise direction).

The same as in chess, stalemate and threefold repetition of position are draws.

Piece moves
In general, forward movement means clockwise direction around the board; backward movement means counterclockwise direction. The squares comprising the board's inner and outer perimeters are called rings. The ring a rook or pawn currently stands on determines its orthogonal forward direction, and for a rook, its orthogonal backward direction. An orthogonal rook move in a direction immediately off its ring is called sideways movement.
 * The king moves the same as the king in chess: one step in any direction. As in chess, a player may not place his king in check. There is no castling in Rollerball.
 * A rook moves any number of steps orthogonally in a straight line in a forward direction, or any number of steps orthogonally sideways. It can also move one step orthogonally backward on its ring. When moving along the outer ring, the rook may "rebound" off a corner square and continue its forward journey at 90 degrees. (Corner squares have 45 degree edges for rebounding.) Only one rebound is permitted for a given rook move.
 * The bishop moves any number of steps diagonally forward, or one step diagonally backward. The bishop may rebound off an outer or inner board edge and continue its forward diagonal journey at 90 degrees. Only one rebound is permitted for a given bishop move.
 * A pawn moves one step orthogonally forward on the ring on which it currently stands, or one step diagonally forward to either ring. A pawn does not move backward or sideways, and there is no initial two-step option. A pawn promotes to rook or bishop when reaching either of the two starting squares of the opponent's pawns.