This is a skillful way to bring speedy orbit shots back under control. As the ball is heading back towards the flipper from an orbit, the player drops the flipper just as the ball hits it. This will cause the ball to stop sharply, bounce off of the flipper and toward the opposite flipper.
At that time, the player may be able to catch and hold it. Or if the ball does not bounce up enough, at least the ball is not moving nearly as fast and the player can try a more measured shot.
See more on The New Pinball Dictionary.