Players in the 1st row pass the ball to each other. Players in the 2nd row must shift in a way that no pass reaches the 3rd row. If a pass reaches the 3rd row, this row tries to pass the ball back to the 1st row.
Tip
Coaching Points
Ball in the center: form a defensive triangle (ball-near player pushes out, outer players tuck in and cover)
Ball on the wings: ball-near player pushes out, other players maintain their level and shift towards the ball