Start the downswing with a touch of downward knee movement
Craig Hanson describes starting the downswing with just a touch of downward movement at the knees rather than exploding from the top. Moving down a little lets you feel pressure into the lead foot, almost like sinking, and he associates it with hitting the ball with a slightly bent arm that has some downward movement.
Channel: CraigHansonGolf
Watch official source at 9:14