Copyright (c) 2001 Vincent Everaert

Under Pressure is played on a 5x5 hexagonal board with the following setup (Black has 26 stones offboard) :

TURNS - .Black plays first.
BLACK SOLDIERS - Black soldiers can move to an adjacent empty hex, providing it keeps a connection with at least one other friendly soldier. A Black’s move cannot break the connection between his soldiers. 
A black soldier offboard can also be dropped to any empty cell adjacent to a friendly stone and non-adjacent to a enemy stone.
WHITE SOLDIERS -  A white soldier can move in any direction to any adjacent empty cell. Men are not forced to stay connected.
CAPTURE - Both soldiers capture in the same way, by jump over opponent’s stones. As in International Checkers, the longest jump is mandatory and captures are mandatory.
KO - Repetition of the position is forbidden for both players.
Black wins if he places or moves a soldier to a cell of the edge of the board.
White wins if he captures all soldiers on the board or stalemate Black.
The game is a draw if Yellow has no more pieces and Red is not on the edge of the board.

Some further notes by the author: 

- An isolated Black stone cannot move, it is stalemated unless it can create a connection with a friendly soldier nearby.
- Black does not win the game if one of its soldiers reaches the border during a jump and if capture is not over. The stone must continue its jump.

An example

Black moves to cell [1] and wins the game. White is forced to capture the other 3 Black stones, and drops one offboard stone at the edge, winning the game 

There is a ZRF to play Under Pressure with Zillions made by Vincent Everaert.