Legal Trap

The Legal Trap or Blackburne Trap 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 Legall. 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
6. Nxe5
6... Bxd1
'''7. Bxf7+ Ke7 8. Nd5'''

Legal versus Saint Brie

The original game featured Legal playing at rook odds 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'''

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, the Legal Trap has ensnared countless unwary players. One author writes that "Blackburne sprang it several hundreds of times during his annual tours."