Keep the torso back so the hands sling like a catapult
The instructor's speed key: do not slide the torso forward through the shot. He explains that moving the body forward drags the grip along with it, leaving the club behind and robbing you of speed. Instead he cues the feeling of the torso staying on the ball while the hands and arms snap in toward the body like a catapult to release the clubhead.
Channel: Danny Maude
Watch official source at 6:16