You will need:
One ball per group. A group of 7-8 students is a good size.
The teacher (or a student) stands in the middle of a small circle. He throws the ball around in the circle in turn. The students must clap their hands before catching the ball. The teacher now throws the ball randomly around the circle. If a student does not grab, they should sit down. If they forget to clap before grabbing the ball, they should sit down. If they clap and the ball does not reach them, they must sit down. The game continues until only one is left.