The Wrong Rook Pawn
The 'wrong rook pawn' is one of the most famous drawing exceptions in all of endgame theory: king, bishop, and an a-pawn or h-pawn against a lone king, which would be an easy win on every other file, is only a draw if the bishop is the wrong color to ever control the pawn's own queening square — and the defending king simply has to reach the corner in time.
Why the corner square's color decides everything
A bishop only ever moves on one color of square for its entire existence. The a8 and h8 corners are light squares; a1 and h1 are dark. If the pawn is heading for a corner that's the OPPOSITE color from the attacking bishop, that bishop can never help control the actual queening square — and without that control, the defending king can simply sit in the corner and can't be dislodged.
Starting position. The wrong rook pawn — a corner the bishop can't touch.
The pawn queens on a light square, but the bishop is dark-squared — it can never touch that corner, and the defending king simply shelters there forever.
Why every other pawn escapes this exception
A pawn on any file other than the a-file or h-file has a queening square that the attacking king can approach from either side — there's room to maneuver, use the bishop to control key squares from a distance, and force the defending king out. On the edge of the board, the pawn's queening square only has one side, and if the bishop's color can't reach it, there's no way around the problem no matter how many extra tempi the attacking side spends.
It doesn't matter how far the pawn advances
Even pushing the pawn to the seventh rank with the king right behind it changes nothing — as long as the defending king reaches the corner before being permanently cut off, the draw holds regardless of the pawn's advancement. The exception is about the bishop's color and the king's timing, not the pawn's progress.
The defending side's one job: get to the corner and stay
For the defender, the entire technique is timing — reach the drawing corner before the attacking king can cut it off, and then simply refuse to be lured away from it. The defending king doesn't need to do anything clever once it's there; it just needs to shuffle between the corner and the one or two adjacent squares that are equally safe.
This is one specific instance of a broader idea
The wrong rook pawn is really just one particular, extremely well-documented example of a fortress — a position the stronger side genuinely cannot break regardless of material. It comes up often enough in real games to deserve its own name, rather than staying a general concept nobody actually recognizes at the board.
Extra pawns change the picture
This whole exception describes the bare king-bishop-and-rook-pawn version specifically. Add even one more pawn anywhere else on the board, on a file the bishop CAN influence, and the attacking side often has entirely new winning tries available — a second passed pawn the defending king can't also blockade, or a distraction elsewhere that pulls the defending king away from the corner at exactly the wrong moment.
For the broader idea this endgame is a specific example of, see fortress positions, and for the related exception in the pure queen-versus-pawn endgame, see queen vs pawn endgame, which has its own rook-and-bishop-pawn drawing exception for a different reason.
Frequently Asked Questions
Does this exception apply to any other pawn besides the a-pawn and h-pawn?
No — it's specific to the two edge files, because only there does the queening square have just one side for the attacking king to approach from. Every other file gives the attacking king enough room to work around a wrong-colored bishop.
What if the attacking side has extra pawns as well as the rook pawn?
Extra pawns on other files usually change the position entirely, since they give the attacking side other ways to make progress or force the defending king away from the corner. This exception specifically describes the bare king, bishop, and single rook-pawn version.
Can the defending king ever be forced out of the corner even in the drawn version?
No, not with correct defense — the whole point of the exception is that there's no way to dislodge a king that's reached the right corner and refuses to leave it, since the bishop structurally can't help control the escape or the queening square.