Get your players to pair up and lie flat on the ground with their legs apart and the soles of their feet touching. Legs should be kept straight and each pair should be given one ball.
The first player holds the ball with straight arms stretched as far behind his head as possible. At the coaches whistle he must rise into an upright position, passing the ball over his head and offering it outstretched to his partner in one fluid motion. The second partner should sit upright to meet the ball and collect it in both hands, Once he has the ball he now reverses the motion his partner just made, slowly returning to a lying position, with the ball passing over his head, until it bumps the ground with arms straight.
As soon as the ball bumps the ground he now rises up again, passing the ball over his head until he offers it to his partner who has remained sitting. The "buck" should be passed at least twenty times.
This warm up gets plenty of the core muscle groups used in soccer stretched out and ready for action. For players with a higher level of fitness, insist that the ball be placed level with the head but to the left or right of the players' body forcing them to work different muscle groups.