Adapted from the package text:
Springline: simple to learn, easy to lose. Springline is a wild, fast moving and unpredictable game of skill and tactics for two, in which moves lead to chain reactions, prisoners return to the game and pieces bounce off the edge of the board.
The board is a hexagonal grid with five spaces along each edge, and is positioned between the players with a corner pointing toward each player. The corner spaces are return pads with the three closest pads belonging to their respective players. There are eight pieces for each player that begin on the three closest return pads, midway between them along the near edges, and two spaces forward of each of the central three pieces. Moves are one space in a straight line or in a hexagonal orbit around any other piece. Three (or more) pieces in a line form a Springline, and either end(s) must discharge before the end of a turn. Discharged pieces travel in a series of straight unobstructed lines (bouncing off the edges of the board as necessary) as far as the player wants. Capture is by replacement, and prisoners are immediately exchanged upon capture. Exchanged prisoners must be re-entered onto one of a player's own vacant return pads at the earliest opportunity. Failure to be able to do so (because they are occupied) loses the game. Alternatively, if a player holds, even for a moment, three opposing prisoners, this wins the game.