The Magnus Smith Trap 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

Chess trap

- List of chess traps :Ordered by chess opening:*Albin Countergambit – Lasker Trap*Blackmar-Diemer Gambit – Halosar Trap*Bogo-Indian Defence – Monticelli Trap*Budapest Gambit – Kieninger Trap...

 in the Sicilian Defence

Sicilian Defence

The Sicilian Defence is a chess opening that begins with the moves:The Sicilian is the most popular and best-scoring response to White's first move 1.e4...

, named after three-time Canadian chess champion

Canadian Chess Championship

This is the list of all the winners of the Canadian Chess Championship, often referred to as the Canadian Closed Championship to distinguish it from the annual Canadian Open tournament. The winner of the Canadian Closed advances to the next stage of the FIDE World Chess Championship cycle...

 Magnus Smith (1869–1934).

The trap occurs in the Sozin Variation, beginning with the moves

1. e4 c5

2. Nf3 d6

3. d4 cxd4

4. Nxd4 Nf6

5. Nc3 Nc6

6. Bc4

This is the Sozin (or Fischer) Variation of the Sicilian Defense.
A common response is 6...e6, to make White's 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...

 on c4 "bite on granite".
By playing 6...g6?!, Black falls into the trap.

6. ... g6?!

7. Nxc6 bxc6

8. e5!

(See diagram.)
Black is in a bad way.
After 8...Nh5?, Bobby Fischer

Bobby Fischer

Robert James "Bobby" Fischer was an American chess Grandmaster and the 11th World Chess Champion. He is widely considered one of the greatest chess players of all time. Fischer was also a best-selling chess author...

 gives 9.Qf3! e6 (9...d5 10.Nxd5!) 10.g4 Ng7 11.Ne4 Qa5+ (11...d5 12.Nf6+ Ke7 13.Qa3+) 12.Bd2 Qxe5 13.Bc3 and Black's queen is trapped.
Preferable alternatives are 8...Ng4 9.e6 f5, and Black eventually managed to draw in Schlechter-Lasker, World Championship (7) 1910 and 8...d5 9.exf6 dxc4 10.Qxd8+ Kxd8 11.Bg5 Be6 12.0-0-0+ Ke8, and Black ultimately even won in Rosen-Burn, Paris 1900.

The move Black actually chooses leads to instant disaster.

8. ... dxe5??

9. Bxf7+

White wins Black's 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...

after 9...Kxf7 10.Qxd8.