Getting quick with the downswing in an attempt to hit it hard and far usually leads to the clubhead casting, commonly referred to "coming over the top".

Complete your backswing with a full shoulder turn, keeping your back to the target as long as possible during your downswing. Start your downswing by allowing your arms to drop. You will soon feel your downswing path coming much more from the inside with a shallow angle of approach into the ball.


Drills:

Tee to ball: Place a tee into the grip end of your club. Begin the downswing by pointing the tee at the ball. This will help establish a proper downswing path.

Gravity drop: Get in your golf posture. Extend your right arm to shoulder height (left for left-handed golfers) and let it fall by force of gravity to your side. Take that same feel to start your downswing.