http://www.thechesswebsite.com/halosar-trap/
The Halosar Trap derives from the Blackmar-Diemer Gambit. In the
Blackmar-Diemer Gambit, white looks to gambit off his king’s pawn on e4.
The most aggressive line (the Ryder Gambit) places the white queen on
f3 and gives away an additional pawn on the d4 square. If black captures
this pawn he is getting closer to falling for the Halosar Trap.
After white responds with Be3, attacking the queen, black is forced
to choose where to move his queen to safety. Many players will choose b4
as it looks like a safe square and it also looks like it can easily
attack the b2 square. Black is not worried about white castling because
his bishop can come to g4 and then pin the queen down to the rook.
This is exactly what white wants black to think and white can
continue with this plan to castle, leaving his queen to be pinned and
instead play Nb5 setting up many great attacking lines for white. Black
is all but lost and will lose considerable material.
Watch the video below to see a detailed explination of this trap.
