The ball is always thrown to a different person, so not to the same person as who gave it to him/her.
When a boy has dropped the ball on the ground, all boys have to run a circle.
When the girls have thrown the ball on the ground then all girls have to run a circle.
As a variation, you can throw in more balls so that the game goes faster and they have to run more often.
You can also give the students numbers 1, 2,. When someone from 1 drops the ball, group 1 runs a circle. When someone from group 2 drops the ball group 2 runs.