Grob Opening

Named after the Swiss master Henri Grob, who played it for decades. Its mirror image, 1. e4 g5, is called the Borg Defense — Grob spelled backwards.

It is reached after a single move: 1. g4.

Black is to move and has 20 legal moves. Over the next four moves — two for each side — the game can branch into 214,048 different games. Those games reach 77,047 different positions: most positions can be reached in more than one way, 2.8 on average.

The Lichess opening list names 19 further lines after this position, such as Grob Gambit (1... d5 2. Bg2) and Zilbermints Gambit (1... d5 2. e4 dxe4 3. Nc3).