Source: Golf Digest
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Eliminate your hook with a simple grip change

A strong grip is by far the most common error I see with players who curve the ball too much from right to left. The right hand drifts to the right–away from the target–and moves underneath the club, as shown in the photograph below. With the right hand in this position, it will tend to turn over too much through impact. Because the position of the right palm roughly replicates the clubface, it’s easy to see why this turning over of the right hand causes the clubface to close and the ball to curve left.

To calm that hook down to a manageable draw, adjust your right hand to a more neutral position, as I’m demonstrating above. Turn it toward the target, so you can’t see your left thumb when you’ve made your completed grip. I also like to put my right index finger in a “trigger” position under the handle, which supports the club through the swing. If the finger wraps around the grip too much, the club tends to get loose at the top.

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