King's Gambit Accepted:Kieseritzky Gambit

Named after Lionel Kieseritzky, the loser of the Immortal Game. White undermines Black’s pawn chain with h4 and Ne5.

It is reached after 9 moves: 1. e4 e5 2. f4 exf4 3. Nf3 g5 4. h4 g4 5. Ne5. It is a line of the King's Gambit Accepted.

Black is to move and has 31 legal moves. Over the next four moves — two for each side — the game can branch into 972,909 different games. Those games reach 331,549 different positions: most positions can be reached in more than one way, 2.9 on average.

The Lichess opening list names 19 further lines after this position, such as Berlin Defense (5... Nf6) and Brentano Defense (5... d5).

The same moves can be played in 70 different legal orders that all reach this position. For example 1. f4 e5 2. e4 exf4 3. Nf3 g5 4. h4 g4 5. Ne5, which starts as the Bird Opening.