This is an open scene that takes place on an imaginary disc.
The players in the scene are encouraged to imagine that the floor of the room is balancing on a fulcrum in the center of the room. If a scene involves one player, they can only stand in the center of the floor. The leader may mark the center of the stage with a safe prop. If the player were to move away from the center of the stage the stage would tip, and she would fall off the stage. If the first player in the scene moves across the stage another player must jump into the scene to keep the stage balanced. The players must keep a balanced distance away from each other. A third players would make the maneuvers on the floor even trickier.
The leader or the audience players can end the scene if the stage becomes unbalanced. This exercise is a good opportunity to tune the players’ listening skills beyond words. Players that become well versed in this exercise can use the whole breadth of the stage in a scene. In essence if a player is prone to sticking in one place on stage. This exercise will get her moving.
Picked this up off the Improv Encyclopedia.