Légal Trap

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This article uses algebraic notation to describe chess moves.

The Légal Trap, 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 Sire de Légal (1702-1792) who was a French player, or Joseph Henry Blackburne (1841–1924), who was a British master and one of the world's strongest players in the latter part of the 19th century.

Contents 1 Natural move sequence 2 Minimum requirements 3 Original game 4 Cheron-Jeanlose 5 Occurrence 6 External links 7 References

[edit] Natural move sequence

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 line in the Philidor Defense.

4. Nc3 Bg4?!

Black apparently pins the knight in the fight over the center. Strategically, this is a sound idea, but there is a tactical flaw with the move.

5. h3

In this position 5.Nxe5? would be an unsound trap. While the white queen still cannot be taken (5...Bxd1??) without succumbing to a checkmate in two moves, 5...Nxe5 would win a knight (for the pawn). Instead, with 5. h3, White "puts the question" to the bishop which must either retreat on the c8-h3 diagonal, capture the knight, be captured, or as in this game, move to an insecure square.

5. ... Bh5?

Black apparently 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. 5...Be6!? is also possible.

6. Nxe5!

The tactical refutation. White seemingly ignores the pin, and surrenders the queen. Black's best course now is to play 6...Nxe5, where with 7.Qxh5 Nxc4 8.Qb5+ followed by 9.Qxc4, White remains a pawn ahead in material, but Black can at least play on. Instead, if Black takes the queen, White has checkmate in two moves:

6. ... Bxd1??

7. Bxf7+ Ke7

8. Nd5# mate

The final position 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.^[1]

[edit] Minimum requirements

In general, any game having a knight on e5 and ending with the moves Bxf7+ Ke7 Nd5# would be called a Légal Mate. Making a "trap" by luring a bishop on g4 or h5 into a queen capture on d1 is not strictly necessary. In order for the last move to be checkmate, it is of course necessary that black have pieces on squares d6, d8, and f8, and that black have no pieces attacking the square d5.

[edit] Original game

The game Légal (playing at rook odds, without Ra1) against St. Brie in Paris around 1750^[2] went as follows:

1. e4 e5

2. Nf3 d6

3. Bc4 Bg4?!

4. Nc3 Nc6

5. Nxe5?! Bxd1??

If Black had instead played 5. ... Nxe5! he would have won a knight 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 à 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. According to Bjerke (Spillet i mitt liv), the Légal Trap has ensnared countless unwary players.

[edit] External links

• Legal Trap at chessgames.com

[edit] References

1. ^ This version of the Légal Trap was presented in Andre Bjerke (1975). Spillet i mitt liv. ISBN 8203079687.  (Norwegian)
2. ^ George Walker: A Selection of Games at Chess, Actually Played by Philidor and His Contemporaries, London 1835, S. 91