No need for setup, just have everyone stand up! A get-up-out-of-your-seat elimination game for the whole group. This is a quick game to wake everyone up and get them involved.
Everyone stands up and faces forward, backwards, left, or right. Then let the crab dance around and land in one of the directions. Anyone facing the same direction of the crab has to sit down. Give everyone a second to face in a different direction and do it again. Keep going until you have two students left. Have them stand on opposite sides of the room and let the crab decide who the winner is.