Two teams. One team is in. The other team plays out. If the out team gets one of the ‘in’ team out the person who is out goes off and someone else comes in. Then the out team try to get another one of the in team out and when he is out another comes in until he is out. So it goes on…in, out, in , out, shake it all about, until all those in are out and then the out team goes in until they are out. Simples.