The game I found is called freeze and Justify. It is a very simple game but is challenging for the actors.
The group should stand or sit around the room or space for acting.
Then two people enter the middle of the room and begin to improvise using as much movement and dialogue as they can.
Then one person in the crowd says “freeze” and the actors have to stop exactly where they were.
Then the person who said freeze taps an actor on the shoulder.
The actor who was tapped sits down and moves to the outside of the area and then the new actor goes into the old actors position.
Then the actors have to create a completely new scene from the positions they are in.
At any moment the crowd can say freeze and it goes again.