The center player C runs backwards and forwards between A and B.
The game starts when C turns toward A and passes the ball.
Now C turns and starts running towards B.
On the way she receives the ball from behind and passes to A.
Then a turn and so on.....
The exercise trains - besides condition - the ability to catch a ball coming from behind. The player must not run sideways but turn the body against the ball while running.
The exercise is very exhausting and must not the exaggerated.