When the Philidor set-up is no longer available, the defending king goes to the short side of the pawn so the rook can check from the long side without being disturbed. A rook check from far away is worth more than a passive king.
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The pawn has reached the fifth rank with the white king beside it on f6, and the Philidor set-up is gone. Your king stands on g8, your rook on a1, and the white rook on b7 threatens a back-rank check followed by the march of the pawn. Black to move, sixteen moves to hold.
What you will learn
01What the short side and the long side of a pawn are, and why your king belongs on the short side.
02Why a rook that checks from four files away cannot be chased or blocked.
03The passive alternative, rook on the back rank, and why it loses.
The technique
An f-pawn splits the board into a short side, the g- and h-files, and a long side, a to e. Your king is already on the short side and stays there, leaving the whole long side to the rook. Distance is what a checking rook needs: from the a-file it checks along any rank, the white king is too far away to attack it, and blocking with the white rook only loses that rook. So the first move is a check from the side, and the checks continue along whichever rank the white king stands on.
If the king walks towards the rook, it leaves the pawn behind. If it tucks itself behind its own rook, your rook returns behind the pawn, ready to check again the moment the king comes out. Where it goes wrong: a rook on the back rank, waiting. The white rook then uses the seventh rank, your king is pushed off g8 or mated, and the pawn walks.
How to practise it
Play Black. A check is the natural first move, and the drill shows quickly if it came from the wrong file. After that, keep the king on g8 and the squares next to it and let the rook travel. A draw after sixteen moves is the pass.
The side of the pawn with fewer files: for an f-pawn, g and h. The defending king goes short so that the rook has the long side for checks.
When does the short-side defence not work?
It needs at least three files between the rook and the pawn; with a central pawn that distance is tight and the defence harder. It also fails if your king is cut off from the queening square.