Casting is when a player uses the hands in the downswing to release the club head too early.
The angle between the club shaft and left arm should remain close to 90 degrees until the shaft passes vertical on the way down.
To get the feel for not using the right hand to release the club early and learn to lag the club we use the arrow drill.
This simple drill will help you feel what happens in the downswing with the hands. Just rest the club shaft against the shoulder and raise the club upwards with the arm as if it was an arrow in its quiver.
To do this you cannot use the right wrist, only the arm can straighten to raise the shaft.
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Filmed at Troon.