Crabs and Crocodiles
To start this game you need a "caller" and two even numbered groups (it is alright if one group has an extra player). The teams stand like so. Place cones, a rope, hoses, shoes, or what ever necessary, on each side, to determine where the opposite team must pass.
The Caller assigns one team (Team 1) as crabs and the other team as crocodiles. When everyone is ready the caller yells either Crabs or Crocodiles. If he/she calls crabs, then the crabs (team 1) try and tag the crocodiles (team 2). Team 2 tries to get across the line behind team 1 (with the two x's). If they cross that line, they remain crocs. If they get tagged, they go to the crabs team. Play continues until they there is one player left on a team. that player (or the last one tagged) gets to be the caller.