Chess Opening Theory/1. d4/1...g5

= 1... g5??: Borg Gambit =

First Impressions
1... g5, the Borg Gambit is a rather rare and unsound response to 1. d5. This move is generally considered inferior to 1... d5 or 1... Nf6 by most masters as Black is giving up a pawn, weakening the kingside defense, and promoting White's development of the queen's side bishop in exchange for developing the king's side bishop in a fianchetto.

Ideas/Responses for White
A controlling move that White can do is 2. e4, taking space in the center and opening up the king's bishop and queen, allowing for rather fast development. The question that White poses on Black is if to continue with the hypermodern idea with 2... Bg7 or try to fight back in the center with 2... d5.

Another move White can do is just take the pawn with 2. Bxg5, allowing for development as well as capturing a pawn. Black may play 2. f6? to kick White's bishop away and gain a tempo, but this can be countered with 3. e4!, making the bishop poisoned by a checkmate with 4. Qh5# if Black greedily takes the bishop with 3...fxg5??.

Center Attack
If White takes the g5 pawn, then there are two main ideas for Black to pursue. Black could go take space in the center with 2...f6 trying to gain tempo and eventually break into the center with 3.e4, also actually kicking the bishop out as the Qg5 checkmate isn't instantaneous now. However, this leads to a devastating attack against Black with Qg5 forcing the king into the open, where White can develop and attack the weak king with Nf6, Bc4, and dxe5.

Fianchetto
Another idea is to fianchetto the bishop if White does not take and to play a pseudo-King's Indian Defense with d6, Nf6, and other hypermodern moves.

Theory table
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1. d4 g5