The whole group lines up at one end of the room.
One person then faces them on the other side of the room.
That person then closes their eyes and runs to the group stopping when they think they have reached the group.
If it looks like the person is not going to stop in time then the overall leader shouts stop (but several metres from the group).
It is important that the overall leader does not take part but observes from the side so their complete concentration is on the runner.
It is also good to give the catching group some simple guidelines for stopping someone i.e Hold arms out in front, stand with legs astride and receive the runner into you hands first, with your body weight forward on the front foot. Make sure your head is positioned to the side so your shoulder will take their weight.
Ask the group how they felt doing the exercise and whether they surprised themselves or not.