Legal Pieces

There are only two legal shapes: a square, and a rectangle that is twice as long as it is wide.

Pieces may have any size, from very small to very large. Because of joins (described below), it's also possible for two pieces to be very close in size, but not quite the same size.

Pieces are either black or white. One player plays the black pieces, the other plays the white.

If, during the course of play, a player wants to use a piece that is not available in the set of pieces they have on the table, it's permissible to take a reasonable amount of time to make the desired piece out of appropriate materials (construction paper, etc). For casual play, players may agree to restrict the legal set of pieces to only those that are available to play with; for competitive play, however, any move producing a legal piece must be allowed.

Starting Position

The standard starting position is a 6x6 checkerboard pattern, with either a black or white piece at the upper left corner. This is called "six by six Crumble". Eight by eight Crumble is also possible, as is any other configuration of starting pieces. The only limit is the agreement between the players. All four-sided starting positions made from the same sized square pieces are named by their length and width, such as six by six, three by five, and so on. Starting positions with different sized pieces or a different overall shape of the playing field may be named by convention between players.

Taking A Turn

The person playing first chooses their color (white or black), and players alternate turns back and forth. Players may not pass, although a draw may be agreed at any time.

Each turn must begin with either a split or a join.

The player's turn may end after the split or join, or at their discretion they may choose to do a swap, starting with one of their newly split or joined pieces.

Winning

If, at any time during the game, one player has a single contiguous block of pieces that touch all four sides of the playing field, that player is the winner.

Here's an example of one of the simplest winning positions possible. It was reached after each player made only two moves:

As you can see, black's pieces form a solid region that connects the top, bottom, left, and right sides together.

"Crumble-Mate"

If one player is unable to prevent their opponent from winning on their next turn, that player is said to be in crumble-mate.

In the above position with white to move, there is no way to prevent black from connecting all four sides.

Unlike in chess, it's not necessary to announce crumble-mate. The game doesn't end at mate, it ends when all four sides are actually connected.

Draw By Repetition

This rule only becomes relevant for more advanced players or formal competitions; if you're just getting to know Crumble, you can ignore it:

With the exception of changes that are elements of the iteration of renewables, if the playing field reaches the same position three times, the game is declared a draw.

Joining

Any cluster of a player's own pieces that would form a single legal-shaped piece if the borders between them were removed, may be replaced by that single larger piece on the playing field.

Here is an example of a before-and-after join. Black is to move:

Before black's move

After black's move. The move notation is: 1,2J3,3

It can be important to remember that there is no minimum increment for differences in piece size. One piece may be only fractionally larger than another. Here is an example of a join that results in a piece that is very close to the size of one of the squares from the starting position:

Before black's move

After black's move. The move notation is: 3,1J2,3

Splitting

If a single straight line (the 'split-line'), cutting through a player's own piece, would produce two legal-shaped pieces, that piece may be replaced by those two smaller pieces, with that split-line marking the border between them.

If the split-line could be extended such that it passed only through the player's own pieces, and only tangentially along the border of any other piece, so as to cut those pieces into two legal-shaped halves, each of those pieces may be replaced by those two smaller pieces, with that line marking the border between them.

The simplest split is through a single piece:

Before white's move

Move colorized for clarity

White has split a single piece. The move notation is: 1,1H

It's also possible to split multiple neighboring pieces, so long as the shared split-line would produce legal pieces:

Before white's move

Move colorized for clarity

White has split two neighboring pieces. The move notation is: 1,1H2

The split-line may also travel along the edges of other pieces, in order to split multiple pieces that are not right next to each other:

Before white's move

Move colorized for clarity

White has split three pieces. The move notation is: 1,1H3

It should be clear from the above examples that a split may affect many pieces across the full length or width of the playing field.

Swapping

Swapping is optional. It may occur only after an initial split or join, and must start with one of the newly split or joined pieces. To perform a single swap, the selected piece may exchange colors with any neighboring opposing piece, if the two corners along the bordering side of one piece also touch the two corners along the bordering side of the other. In other words, if the two pieces each border the other along the full length of the bordering side. In the crumble universe, the two pieces are understood to change color simultaneously.

Before black's move

Move colorized for clarity

Black has split a piece and swapped to a neighboring piece. the move notation is: 2,1VE

Having performed a single swap, the piece that has newly become the player's own color may swap again with any neighboring piece meeting the above conditions, as part of the same turn. This chain of swaps may continue as far as the player wants to take it, so long as the above conditions are met.

Before black's move

Move colorized for clarity

Black has split a small square and swapped through several white pieces The move notation is: 2,3,1VWNEENNWW

Since swapping is the only way that colors change location in Crumble, a player can only win as the result of a swap, either by themselves or by their opponent. Swapping is also the only way to perform captures, as discussed below:

Capturing

Any ring of contiguous pieces of one color that contain pieces of the opposing color within them, cause those opposing pieces to immediately be converted to the color of the capturing ring of pieces. Captures cannot occur on the edge of the board - the captured pieces must be completely surrounded by the opposing forces.

Before black's move

Move colorized for clarity. The captured piece is outlined in red

Black has split a small square, and swapped around to capture a small white rectangle. The move notation is: 2,2VWNE

Multiple captures may happen on a single turn, as a player swaps their piece into different positions before their turn ends. On a single turn, a player's own pieces may be captured, and multiple groups of pieces may be captured in different locations on the same turn.

Before black's move

Move colorized for clarity. The captured pieces are both outlined in red

Black has split a small square, and swapped around to first capture a small white rectangle, and then continued swapping to capture a larger white rectangle. the move notation is: 2,2VWNENEES

Sometimes, having swapped a piece into a location to perform a capture, a player might want to swap back along the same path, to end up at a different location. This is allowed.

Before black's move

Move colorized for clarity. The captured pieces are both outlined in red.

Black has split a small square, swapped around to capture pieces in two locations, and then swapped back up through a piece that had already been swapped through, to arrive at the final position. The move notation is: 2,2VWNENEESNNNWW

Note that it is possible to capture the very piece engaged in the swap-chain. This kind of self-capture results in the immediate end of the player's turn.

Before black's move

Move colorized for clarity. The black piece was captured at the spot outlined in red.

Black has split a small square and swapped upwards. At that point, the piece has swapped into a position where it is entirely surrounded by white pieces. It is thus captured, and black's turn ends. The move notation is: 2,3,1HN

Summary

• Legal Pieces
• Either black or white (no mix of color)
• Square
• Rectangle twice as long as wide
• May have any size up to the size of the playing field
• May be constructed by appropriate materials in a reasonable amount of time if unavailable during play
• Starting position
• 6x6 checkerboard pattern, called "6 by 6 Crumble"
• Any starting position is permissible, by agreement between players
• Taking turns
• The player who plays first picks which color to play
• Players alternate back and forth
• Players may not pass
• Each turn must start with either a split or a join
• The player may optionally do a swap with one of the newly split or joined pieces
• Winning
• At any time during the game, a single contiguous block of one player's pieces, touching all four sides of the playing field
• "Crumble mate" is a position where a player cannot prevent the opponent from winning on the next move
• "Crumble mate" doesn't need to be announced
• Draw by repetition
• Discounting changes that are the elements of the iteration of renewables, if the position repeats itself three times the game is declared a draw.
• Joining
• A player may only join their own pieces
• Any cluster of pieces may be replaced by a single larger piece, if that piece would have a legal shape
• Splitting
• A player may only split their own pieces
• Any number of pieces may be split with a single straight split-line, if that split-line:
• would produce all legal shaped pieces
• may pass along the border of any piece, including opposing pieces
• does not pass through any piece that will not be split
• Swapping
• Is optional
• Must come after a split or join
• Must involve one of the newly split or joined pieces
• The selected piece may exchange colors with any opposing piece that has two of its corners touching the corners of that piece
• The selected piece may swap again from its new position with any eligible opposing neighbors, and may continue to swap as many times as the player wants, even ending up in the same location it started from
• Capturing
• Any group of pieces that are entirely surrounded by a contiguous ring of opposing pieces, become the opponent's color.
• Captures are assessed after each step in a chain of swaps
• If the swapping piece moves into a position where it would be captured, it is captured, and the player's turn immediately ends
• Note: A player's pieces may be captured on either player's turn
• Note: Multiple captures may occur during a single turn