Blackmar-Diemer Gambit, Halosar Trap

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

Black falls into the trap with 7...Bg4??

The Halosar Trap (named after Hermann Halosar) is a chess opening trap in the Blackmar–Diemer Gambit.

Analysis

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

5. Qxf3?! Qxd4 6. Be3 Qb4?!

Better is 6...Qg4. Black thinks that castling is prevented because of ...Bg4, but White castles anyway.

7. 0-0-0 Bg4?? (see diagram)

Blundering into the trap.

8. Nb5!!

White threatens mate with 9.Nxc7#. The black queen cannot capture the knight because 8...Qxb5 9.Bxb5+ is check, gaining time for the white queen to escape the black Bg4's attack.

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 (diagram)

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

Position after 11...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.

References

• Burgess, Graham (2009). The Mammoth Book of Chess (3rd ed.). Running Press. ISBN 978-0-7624-3726-9. p. 202-3