The bottleneck is a strategic formation in the game of Hex where one player blocks the opponent's progress by occupying key positions on the board, creating a narrow passage that is difficult for the opponent to break through. The board fragment shown below illustrates this concept, with Blue occupying the key positions in a bottleneck formation, hindering Red's ability to connect to the bottom of the board.
This formation often leads to a ladder, with Red getting ladders in both directions, as shown in the second board fragment.
It's important to note that, although the bottleneck can be an effective defense strategy, it also has its own weaknesses and can be exploited by a skilled opponent. Knowing how to both create and counter bottleneck formations is an important aspect of mastering the game of Hex.