When a fast break is performed it happens that 1st wave cannot take a free shot.
Then the ball is passed backwards to the 2nd wave, but the 1st wave must not stop their attack.
They must continue and use the "panic" in the defense in order to reach a free position in such a way, that the 2nd wave can break through or pass to one of the waiting 1st wave players.

In the shown example the CB pass the ball to the goal keeper.
At the same time the 2 wings rush forward.
The goal keeper throws the ball to one of the wings, who breaks inward and receives the ball.
The defending player closest to this wing moves forward to defend. 
The wing passes the ball back to the CB who is the 2nd wave and continues against the goal circle
If the defender chooses to cover the wing, the CB can shoot.
If the defender covers CB, the wing must move in to a free position at the goal circle and be able to receive the ball from CB.
If the second defender moves in to defend, the second wing will be free.

It is important in this exercise that the 1st wave don't stop near the 9-meter throw line, but moves into a good position at the goal circle.