History
The trap is named after the 18th-century French player Kermur de Légal, the teacher of the famous Philidor. It is more than two hundred years old, yet amateurs still fall for it.
How the mate is delivered
1. 2. 3. 4. 5. 6. 7.
The key moments:
- 3… Bg4 — Black pins the knight on f3 to the white queen. It looks as if the knight cannot move.
- 4… g6? — a weak move. Black wastes time, and f7 is still defended only by the king.
- 5. Nxe5! — White breaks the “pin” and gives up the queen.
- 5… Bxd1?? — the decisive mistake. Black takes the queen — and gets mated.
- 6. Bxf7+ Ke7 7. Nd5# — the king is surrounded by its own pieces, and three white minor pieces cover all its squares.
Why it works
Black was carried away by the pin and forgot that it is not absolute: behind the knight stood the queen, not the king, so the knight was allowed to move. Besides, f7 is weak — only the king defends it, just as in Scholar's mate.
How not to fall into the trap
If your opponent “hangs” the queen, stop and ask yourself why. Instead of 5… Bxd1 Black should have played 5… dxe5, winning back the knight and ending up only a pawn down.
The general rule: before grabbing “free” material, check your opponent's checks and captures after that move.
Try it yourself
White to move. Mate in 1
Show solution
7. Nd5# — the knight on d5 gives check. The squares d7 and f7 are covered by the knight on e5, e6 and e8 by the bishop on f7, f6 by the knight on d5, and d6, d8 and f8 are occupied by Black's own pieces.