Rules 07: Illegal positions
7.1. (a) If during a game it is found that the initial position of the pieces was incorrect, the game shall be cancelled and a new game played.
(b) If during a game it is found that the only error is that the chessboard has been placed contrary to Article 2.1, the game continues but the position reached must be transferred to a correctly placed chessboard.
7.2. If a game has begun with colours reversed then it shall continue, unless the arbiter rules otherwise.
7.3. If a player displaces one or more pieces, he shall re-establish the correct position on his own time. If necessary the opponent has the right to restart the player's clock without making a move in order to make sure the player re-establishes the correct position on his own time.
7.4. If during a game it is found that an illegal move has been made, or that pieces have been displaced from their squares, the position before the irregularity shall be re-instated. If the position immediately before the irregularity cannot be identified the game shall continue from the last identifiable position prior to the irregularity. The clocks shall be adjusted according to Article 6.13 and, in the case of an illegal move, Article 4.3 applies to the move replacing the illegal move. The game shall then continue.