Assume 2 teams
Person 1 throws the ball over the net (width of the field) person 2 catches the ball, person 1 moves 2 steps sideways.
Person 2 throws in the ball and person 1 catches the ball. Person 2 now moves 4 steps, etc.
Variations: throw the ball on to the 3 meter line, throw the ball on to the 7 meter line and walk back to the 3 meter line, pass the ball on to the other person and the other person passes on the ball to him/herself and catches it.