#1 passes to #3 and follows, #1 gets the ball back from #3, #1 either has to stop 1-2 or a jumpstop, then #1 makes a back pivot and opens to the middle, at the same time #2 and #4 are doing the same thing - continuation see next frame
 

after #1 opened to the middle #3 is runing around and getting the ball from a handoff from #1 and passes the ball to the next one in the line at the next station and now everything starts from the beginning;

to make it more difficult you can put 4 balls instead of two, another difficulty is if you make them switch the direction on your wisstle