Three Moves Rule
(Lake Charles, Louisiana, USA)
Q. I've heard about a way to draw in chess if you're losing. It's called the 3 moves rule. I'm having a hard time understanding the 3 moves rule in a chess game and how it plays out to be a draw. How does it work?
A. That would be the three times repetition rule. If pieces of the same kind and of the same color occupy the same squares, but the possibilities for moving these pieces are not the same, then the player moving cannot claim a draw.
For example, you would no longer be entitled to demand a draw if, after the repetition of a position, castling or taking a pawn "en passant" was no longer possible.
However if the same pieces and pawns occupy the same squares with the same person to move, and the possibilities for castling and/or en passant are the same, then you can draw under the 3 Times Repetition Move. The important thing is that you reach the exact same position with the exact same circumstances 3 times.
You may only propose a draw when you have just completed a move. You start your opponents clock after the request, not before. Your opponent may accept the draw or, either orally or by completing a move, he may reject it. In the meantime you cannot withdraw it.
You can read more here and here.