The Légal Trap or Blackburne Trap (also known as Légal Pseudo-Sacrifice and Légal Mate) is a chess opening, characterized by a queen sacrifice followed by checkmate involving three minor pieces if Black accepts the sacrifice. The trap is named after the French player Sire de Légall. Joseph Henry Blackburne, 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.

Natural move sequence

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. e4 e5 2. Nf3 Nc6 3. Bc4 d6''' 4. Nc3 Bg4 5. h3 5... Bh5 (diagram) 6. Nxe5 6... Bxd1 '''7. Bxf7+ Ke7 8. Nd5'''

Légal versus Saint Brie

The original game featured Légal playing at rook odds (without Ra1) against Saint Brie in Paris 1750: '''1. e4 e5 2. Nf3 d6 3. Bc4 Bg4?! 4. Nc3 g6? 5. Nxe5 Bxd1?? 6. Bxf7+ Ke7 7. Nd5# ''' '''1. e4 e5 2. Bc4 d6 3. Nf3 Nc6 4. Nc3 Bg4 5. Nxe5? Bxd1?? 6. Bxf7+ Ke7 7. Nd5# 1–0'''

Other variations

Considerations

A mating pattern where a pinned knight moves, allowing the capture of the player's queen but leading to a checkmate with three minor pieces, 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."