The Legal Trap, Blackburne Trap, also known as Legal Pseudo-Sacrifice and Legal Mate is a chess opening

Chess opening

A chess opening is the group of initial moves of a chess game. Recognized sequences of opening moves are referred to as openings as initiated by White or defenses, as created in reply by Black. There are many dozens of different openings, and hundreds of named variants. The Oxford Companion to...

 trap, characterized by a queen

Queen (chess)

The queen is the most powerful piece in the game of chess, able to move any number of squares vertically, horizontally, or diagonally. Each player starts the game with one queen, placed in the middle of the first rank next to the king. With the chessboard oriented correctly, the white queen starts...

 sacrifice

Sacrifice (chess)

In chess, a sacrifice is a move giving up a piece in the hopes of gaining tactical or positional compensation in other forms. A sacrifice could also be a deliberate exchange of a chess piece of higher value for an opponent's piece of lower value....

 followed by checkmate with minor pieces if Black accepts the sacrifice. The trap is named after Sire de Légal

Legall de Kermeur

Legall de Kermeur was a French chess player.His name is variously written Kermur, Sire de Legalle, by Twiss, and Kermur and Kermuy, Sire de Legal, by others...

 (1702–1792), a French player. Joseph Henry Blackburne

Joseph Henry Blackburne

Joseph Henry Blackburne , nicknamed "The Black Death", dominated British chess during the latter part of the 19th century. He learned the game at the relatively late age of 18 but quickly became a strong player and went on to develop a professional chess career that spanned over 50 years...

 (1841–1924) was a British master, and one of the world's strongest players in the latter part of the 19th century.

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

Italian Game

The Italian Game is a family of chess openings beginning with the moves:The game's defining move is the White king's bishop's move to c4 in preparation for an early attack on Black's vulnerable f7-square. As such the game is typified by aggressive play, where Black's best chances are often...

, it is somewhat passive, and transposes to a line in the Philidor Defense.

4. Nc3 Bg4?!

Punctuation (chess)

When annotating chess games, commentators frequently use question marks and exclamation points to denote a move as bad or good. The symbols normally used are "??", "?", "?!", "!?", "!", and "!!". The corresponding symbol is juxtaposed in the text immediately after the move When annotating chess...

Black apparently pin

Pin (chess)

In chess, a pin is a situation brought on by an attacking piece in which a defending piece cannot move without exposing a more valuable defending piece on its other side to capture by the attacking piece...

s the knight

Knight (chess)

The knight is a piece in the game of chess, representing a knight . It is normally represented by a horse's head and neck. Each player starts with two knights, which begin on the row closest to the player, one square from the corner...

 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

Bishop (chess)

A bishop is a piece in the board game of chess. Each player begins the game with two bishops. One starts between the king's knight and the king, the other between the queen's knight and the queen...

 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

Pawn (chess)

The pawn is the most numerous and weakest piece in the game of chess, historically representing infantry, or more particularly armed peasants or pikemen. Each player begins the game with eight pawns, one on each square of the rank immediately in front of the other pieces...

. 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

Queen (chess)

The queen is the most powerful piece in the game of chess, able to move any number of squares vertically, horizontally, or diagonally. Each player starts the game with one queen, placed in the middle of the first rank next to the king. With the chessboard oriented correctly, the white queen starts...

. 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

Checkmate

Checkmate is a situation in chess in which one player's king is threatened with capture and there is no way to meet that threat. Or, simply put, the king is under direct attack and cannot avoid being captured...

The final position is a pure mate

Pure mate

A pure mate is a checkmating position in chess in which the mated king and all vacant squares in its field are attacked only once, and squares in the king's field occupied by friendly units are not also attacked by the mating side .Such a mate occurred in the...

, meaning that for each of the eight squares around the black king, there is exactly one reason the king cannot move there.

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.)

In games

The original game was Légal (playing at rook odds

Chess handicap

A handicap in chess is a way to enable a weaker player to have a chance of winning against a stronger one. There are many kinds of such handicaps, such as material odds, extra moves A handicap (or "odds") in chess is a way to enable a weaker player to have a chance of winning against a stronger...

, without Ra1) against Saint Brie in Paris

Paris

Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

 1750, went as follows:

1. e4 e5

2. Nf3 d6

3. Bc4 Bg4?!

4. Nc3 g6

5. Nxe5 Bxd1?

6. Bxf7+ Ke7

7. Nd5#

Cheron versus Jeanlose

At a simultaneous exhibition

Simultaneous exhibition

A simultaneous exhibition or simultaneous display is a board game exhibition in which one player plays multiple games at a time with a number of other players. Such an exhibition is often referred to simply as a "simul".In a regular simul, no chess clocks are used...

 in Paris, André Cheron

André Chéron

André Chéron was a French chess player, endgame theorist, and a composer of endgame studies. He lived in Switzerland for many years...

, one of France's leading players, played a similar trap in the game Cheron vs. Jeanlose.

1. e4 e5

2. Nf3 d6

3. Bc4 Nc6

4. Nc3 Bg4?!

5. h3! Bh5?

6. Nxe5!

If 6. ... Nxe5 7. Qxh5 Nxc4 8. Qb5+ wins the knight.

6. ... Bxd1??

7. Bxf7+ Ke7

8. Nd5#

Other variations

Sometimes the mate can be administered by a different piece. This game came from the Petrov's Defence

Petrov's Defence

Petrov's Defence is a chess opening characterised by the following moves:Though this symmetrical response has a long history, it was first popularised by Alexander Petrov, a Russian chess player of the mid-19th century...

; and is very old:

1. e4 e5 2. Nf3 Nf6 3. Nxe5 Nc6?! 4. Nxc6 dxc6 5. d3 Bc5 6. Bg5? Nxe4 7. Bxd8?? Bxf2+ 8. Ke2 Bg4#

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. One author writes that "Blackburne sprang it several hundreds of times during his annual tours."

External links

• Legal Trap at ChessGames.com