This exercise can be extended, so 3 or more balls can be in use at the same time. However start with only 1 ball.
All the players are moving forward when they receive the ball.
LW passes the ball to LB, who passes to CB, who passes to RB, who passes to RW, who passes to the "goalkeeper", who passes to LW.
LB runs after the pass to CB's position.
CB to RB's position and RB runs to LB's position.
The wings and the "goalkeeper makes piston movements forward and backwards all the time.
An extra player can be put into action on those positions when more balls come into action.