Légal Trap

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This article uses algebraic notation to describe chess moves.

The Légal Trap or Blackburne Trap is a chess opening trap. Sire de Légal (1702-1792) was a French player, while Joseph Henry Blackburne (1841–1924) was a British master, and one of the world's strongest players in the latter part of the 19th century. There are a number of ways the trap can arise, one of them being:

1. e4 e5

2. Nf3 Nc6

3. Bc4 d6

While 3...d6 is a playable answer to the Italian Game, it is somewhat passive, and transposes to a form of the Philidor Defense.

4. Nc3 Bg4?!

Black pins the knight in the fight over the center. Strategically this is a good move, but there is a tactical flaw.

5. h3

In this position 5.Nxe5? would be an unsound trap. Black could not take White's queen without succumbing to a checkmate in two moves, but 5...Nxe5 would win a knight. Instead, White "puts the question" to the bishop which must either retreat, capture the knight, or as in this game, move the bishop to an insecure square.

5. ... Bh5?

Black maintains the pin, but this is a tactical blunder which loses at least a pawn. Relatively best is 5...Bxf3, surrendering the bishop pair, and giving White a comfortable lead in development, but maintaining material equality, or 5...Be6!?

6. Nxe5!

The tactical refutation. White seemingly ignores the pin, and surrenders the queen. Black should now play 6...Nxe5 7.Qxh5 Nxc4 8.Qb5+ followed by 9.Qxc4, when White has won a pawn, but Black can play on. Instead, if Black takes the queen, White will win in two more moves.

6. ... Bxd1??

7. Bxf7+ Ke7

8. Nd5 mate

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

[edit] Original game

The game Légal played against St Brie in Paris in 1750 ran:

1. e4 e5

2. Nf3 d6

3. Bc4 Bg4?!

4. Nc3 Nc6

At this point Légal, according to spectators, put his finger on the Nf3, then quickly took it off. The spectators reminded him of the touch-move rule and said that he had to move it. Légal said that he knew that, and he was just trying to figure out where to move it. Setting an unsound trap, he then played:

5. Nxe5?! Bxd1??

If Black had played 5. ... Nxe5! he would have won a piece for a pawn. Now mate follows in two moves.

6. Bxf7+ Ke7

7. Nd5#

[edit] Cheron--Jeanlose

At a simultaneous exhibition in Paris, André Cheron, one of France's leading players, played a similar but sound trap in the game Cheron--Jeanlose.

1. e4 e5

2. Nf3 d6

3. Bc4 Nc6

4. Nc3 Bg4?!

At this point the game deviates from Légal--St Brie. Cheron played:

5. h3! Bh5?

6. Nxe5!

Now this sacrifice á la Légal is perfectly sound. If 6. ... Nxe5 7. Qxh5 Nxc4 8. Qb5+ wins the knight. The move Jeanlose played, instead of losing a pawn, loses the game.

6. ... Bxd1??

7. Bxf7+ Ke7

8. Nd5#

[edit] Occurrence

This kind of mate, where an apparently pinned knight moves anyway, allowing capture of the queen, but leading to a checkmate with both knights and a bishop, occasionally occurs at lower levels of play, though masters would not normally fall for it.