Wrong rook pawn

In a chess endgame of a king, bishop, and pawn versus king, a wrong rook pawn is a rook pawn (a pawn on the a- or h-file) whose promotion square is the opposite color from the bishop's square color. Since a side's rook pawns promote on opposite-colored squares, one of them may be the "wrong rook pawn".^[1] This situation is also known as having the wrong-colored bishop or wrong bishop (i.e. the bishop is on the wrong-colored squares in relation to the rook pawn).^[2] In many cases, the wrong rook pawn will only draw, when any other pawn would win. This is because the defending side can sometimes get their king to the corner in front of the pawn, after which the attacking side cannot chase the king away to enable promotion. A fairly common defensive tactic is to reach one of these drawn endgames, often through a sacrifice.

In some endgames, such as bishop and pawn versus king (perhaps with pawns), the wrong rook pawn is the one whose promotion square is opposite the color on which the bishop moves, which makes the stronger side unable to win. This was known at least as early as 1623, as evidenced by an endgame study by Gioachino Greco.

A less common situation is the defense of bishop versus rook and rook pawn; the wrong rook pawn is the one that promotes on the square not controlled by the bishop, because the defending king and bishop can form a blockade in the corner (on the pawn's promotion square) and draw the game. This is also called the safe corner for the defending king.