Grob Opening

The Grob begins with 1.g4: the pawn from g2 advances two squares. White gains space on the kingside, the half of the board where the king starts, and clears g2 for the f1-bishop. After that bishop reaches g2, it can work along a long diagonal toward the center and queenside.

The problem is that the g-pawn is part of the king's natural shelter. Advancing it to g4 exposes squares and diagonals around the position White's king would occupy after kingside castling, the special move that places the king on g1 and rook on f1. At the same time, the g4-pawn occupies none of the four central squares d4, e4, d5, and e5. Black can exploit this by occupying the center with pawns and bringing pieces out from their starting squares.

The Grob contains gambits, meaning voluntary pawn offers made to gain activity, as well as tactical traps. Those possibilities do not make the first move strategically safe. Compared with the Polish Opening, both openings push a wing pawn two squares and prepare a bishop for a long diagonal; the critical difference is that the g-pawn sits much closer to White's king.

The Grob allows ...d5 and offers a risky gambit

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Startg4d5Bg2Bxg4c4

The g-pawn belongs to the king's future shelter

Moving it can prepare the bishop but immediately changes the squares around kingside castling.