The Halosar 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 Blackmar-Diemer Gambit

Blackmar-Diemer Gambit

The Blackmar–Diemer Gambit is a chess opening characterized by the moves:- History :The Blackmar–Diemer Gambit arose as a development of the earlier Blackmar Gambit, named after Armand Blackmar, a relatively little-known New Orleans player of the late 19th century who popularized its...

.

The trap begins with the moves

1. d4 d5

2. e4

This is the start of the Blackmar-Diemer Gambit.

2. ... dxe4

3. Nc3 Nf6

4. f3 exf3

Now 5.Nxf3 is usual, but by capturing with 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...

, White lays a trap. (This is the Ryder Gambit.)

5. Qxf3 Qxd4

6. Be3 Qb4?!

Better is 6...Qg4.
Black thinks that castling

Castling

Castling is a special move in the game of chess involving the king and either of the original rooks of the same color. It is the only move in chess in which a player moves two pieces at the same time. Castling consists of moving the king two squares towards a rook on the player's first rank, then...

 is prevented because of ...Bg4, but White castles anyway.

7. 0-0-0 Bg4?

(See diagram.)
Blundering

Blunder (chess)

In chess, a blunder is a very bad move. It is usually caused by some tactical oversight, whether from time trouble, overconfidence or carelessness. While a blunder may seem like a stroke of luck for the opposing player, some chess players give their opponent plenty of opportunities to blunder.What...

 into the trap.

8. Nb5!!

White threatens mate with 9.Nxc7#. The Black queen can't capture 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...

 because 8...Qxb5 9.Bxb5+ is check and loses the queen.

8. ... Na6

9. Qxb7 Qe4

Black lost even more quickly in Diemer-Halosar, Baden-Baden 1934, after 9...Rc8 10.Qxa6 1-0.

10. Qxa6 Qxe3+

Worse is 10...Bxd1 11.Kxd1 Rd8+ 12.Bd2 and White is winning, for example 12...Ng4 13.Nxc7+ Kd7 14.Qxa7.

11. Kb1 Qc5

12. Nf3

The White threat of 13.Qb7 wins the black a-pawn by force. With even material and a passed a-pawn, White will have a winning advantage (Burgess). Even stronger seems 12. Qb7! with the idea 12. ... Bxd1 13. Qxa8+ Kd7 14. Nc3 and White has a winning attack.