The players throw the balls hard on the floor at the same time so that they jump to chest height or head height.
Then they perform a fast sideway stepping and must catch the fellow players’ ball before it hits the floor.
The balls are thrown on the floor again and both players move back again to catch the balls.

The exercise can also be performed in this way:
The players stand in some distance of each other.
The balls are thrown forward in a soft curve at the same time.
Both players must then move quickly sideways and catch each others ball.
Then throw and back again.