Légal's mate

The Légal Trap or Blackburne Trap (also known as Légal Pseudo-Sacrifice and Légal Mate) is a chess opening trap, characterized by a queen sacrifice followed by checkmate with minor pieces if Black accepts the sacrifice. The trap is named after the French player Sire de Légal (1702–1792). Joseph Henry Blackburne (1841–1924), a British master and one of the world's top five players in the latter part of the 19th century, set the trap on many occasions.

There are a number of ways the trap can arise, the one below shows a natural move sequence from a simultaneous exhibition in Paris. André Cheron, one of France's leading players, won with the trap as White against Jeanlose:

1. 2. 3.

4. Nc3 Bg4?!

5. h3

5... Bh5? (see diagram)

6. Nxe5!

6... Bxd1?? 7. Bxf7+ Ke7 8. Nd5#

The final position (see diagram) is a pure mate, meaning that for each of the eight squares around the black king, there is exactly one reason the king cannot move there.

The original game featured Légal playing at rook odds (without Ra1) against Saint Brie in Paris 1750:

Note: The above move order is found in most publications; however, research published at ChessBase suggests that the move order has been altered retrospectively in order to remove a flaw in the original game. Also the year 1750 is assumed to be wrong; it is more likely that the game was played in 1787, and that the original move order was:

Here the combination is flawed, as with 5... Nxe5 Black could have gained a piece. It is reported that Légal disguised his trap with a psychological trick: he first touched the knight on f3 and then retreated his hand as if realizing only now that the knight was pinned. Then, after his opponent reminded him of the touch-move rule, he played Nxe5, and the opponent grabbed the queen without thinking twice.

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Wikipedia