How Koga decides
- We capture a pawn that is shielding the enemy king, giving up a piece worth more than the pawn we take.
- The point is not the pawn itself — it is to tear a hole in the wall of pawns in front of the king so our other pieces can pour in.
- The classic shape is the Greek gift: a bishop or knight crashes into f7/h7 (or the queenside equivalent) right next to the uncastled or castled king.
- The captured pawn must sit on a shield square: one of the two ranks directly in front of the enemy king's back rank.
- It must also be close to the king — on the king's file or one of the two files beside it.
- Squares like f7, g7, h7 (or a7, b7, c7) for a black king on the back rank are the typical targets.
- The move must be a capture, and the capturing piece must be worth strictly MORE than the pawn it takes — we are deliberately giving up material to open the king.
- It must be a real sacrifice: after the capture, the other side must attack the capture square. If no enemy piece attacks it, the capture just wins material (Hanging Piece). A king capture is never Destroying, because a king can't capture onto an attacked square.
- We check only that the square is attacked, not that the recapture is legal right now: an attacker that is pinned still counts.
- The enemy king is the exception: it counts only if it may legally take back. If our other pieces guard the square, the king can't recapture, so the capture is just a free pawn, not a sacrifice.
- There must be at least one OTHER friendly piece (knight, bishop, rook, or queen) still on the board to exploit the exposed king. A lone sacrificer with no follow-up support is not flagged.
- We judge only the geometry, the material given up, whether the square is attacked, and the presence of a follow-up piece — we do not separately prove the sacrifice is objectively sound.
Test positions (the examples that guard against regressions)
Knight crashes into f7
From the game kwGLefOd. White plays Nxf7, giving up the knight to rip open the black king's f7 shield. The knight is worth more than the pawn it takes, the black king sits right beside f7, and other white pieces remain to exploit the open king — so Koga calls this a destroying sacrifice. The geometric fork on the same move is demoted, because the king simply takes the undefended knight for free.
Greek gift on f7
A constructed Greek-gift position. The bishop captures on f7, giving up the bishop for a single pawn to shatter the shield in front of the black king on e8. With other white pieces ready to join the attack, Koga flags the destroying sacrifice.
Bishop takes the f3 shield pawn
From the game Cw2pV8jL. Black plays Bxf3, giving up the bishop for the pawn in front of the white king on g1. The g2 pawn attacks f3, so the bishop is en prise: it is a real sacrifice. The g2 pawn is pinned by the rook on g8 for now, but Koga asks only whether the square is attacked, so it flags the destroying sacrifice.
Bishop takes h7 — the king may take back
From Tactics Ninja puzzle 19660. White plays Bxh7+, giving up the bishop for the h7 pawn in front of the black king on g8. No white piece guards h7, so Kxh7 is legal: the bishop is a real sacrifice, and Koga flags the destroying sacrifice.
Rook takes the f3 shield knight
From Lichess puzzle 000h0. Black plays Rxf3, giving up the rook for the knight that shields the white king on g1. After gxf3 the black queen enters with Qxh2+. The shield piece is a knight, not a pawn, but the king's cover is still torn open, so Koga flags the destroying sacrifice.
Queen takes f7 — the king can't take back
From Lichess puzzle 007tv. White plays Qxf7+. Only the black king on e8 touches f7, but the bishop on c4 guards f7, so Kxf7 is illegal. The queen is never at risk: White wins a pawn with check. That is not a sacrifice, so it is not Destroying.
King takes a hanging rook — not Destroying
From the game H1T0Nipt, move 49. White plays Rd3?? and the black king takes the rook: Kxd3. The capture lands next to the white king on c1, but nothing can take back on d3, so Black gives up nothing. That is a free rook (Hanging Piece), not a destroying sacrifice.