The players are divided into two teams: hats or no hats or any other distinctive mark. There are no limitations to the ground to be covered.
The object is for the players of each side to throw the ball to one another, without letting it fall to the ground. This has to be done ten times in a row. The players count aloud. The opposite team tries to get the ball and, in turn, must throw it to one another ten times in a row.
Rules The ball may not be taken from the hands of an opposing player; it may only be intercepted in the air or picked up from the ground. The ball may not be thrown back to the same player who threw it, therefore you need at least three players on each team. A player may not run with the ball in her hands.
Each time the "referee" blows her whistle to signal a mistake (ball thrown back to the person who threw it, running with the ball etc.), the ball goes to the opposite team.