There are almost as many theories about the golf swing as there are instructors. And one of the least understood aspects of the swing is the rotation of the hips to an “open” position just before impact.
Most contemporary golf instructors believe it is necessary to “clear your hips just before the point of impact” in order to get your hips out of the way of your hands. According to this theory, if you don't “clear your hips” your hands and arms will be impeded and will not be able to attack the ball with power.
This is sometimes used as an explanation for why an overly “vertical” stance is not a good thing. According to this line of thinking, when you stand too close to the ball your hands will not be able to make a clean pass in front of your body because on the way down your hips will get in the way.
But while hip rotation is very important to the effectiveness of the golf swing, it is not because the hips are in the way of anything. In fact I can't see that this idea of “clearing the hips” makes much sense. Your hips are not in the way of your hands. In fact, rotating your hips towards the target pushes your backside out further towards your hands and puts your hips more in the way than if you did not rotate them.
Most of us — whether we rotate a lot or not — are not in the habit of hitting our hips with our hands when we swing our golf clubs. The reason is simple: our hips do not get in the way of our swing, and to suggest this as an explanation of the importance of hip rotation is just plain misleading.
In my own research, on the course and in my basement “lab”, I have found that hip rotation does indeed put the club on a more powerful, more direct path to the ball coming into the point of impact. But as far as I can tell, this has very little to do with getting your hips out of the way of your hands.
What happens when you rotate your hips is that this allows you to get your shoulders and arms in the optimal power position. This happens because your upper body and lower body move in a synchronized way. In the golf swing, as in most other movements involving the human body, your upper body, including your shoulders and arms, moves in harmony with and in response to the movement of your lower body — your hips and legs.
Think of a power hitter in baseball. Those classic photographs of Ted Williams, Hank Aaron, Reggie Jackson or Barry Bonds making contact with the ball always tell the same story. Their arms are fully extended, hips are rotated to an open position, head is back, and they are perfectly balanced with most of their weight now centered over their front leg and hip. In fact they have used their front leg and hip as a pivot around which their upper body has rotated. Take that pivot away — swing with just your shoulders and arms — and you're left with a much less fluid, much less coordinated, and much less powerful swing.
In the golf swing this connection of upper and lower body is less obvious because the golf swing is a combination of vertical and horizontal. But the principle is the same. The rotation of the hips pulls your upper torso around and gets your lead shoulder into the correct position (the left shoulder in the case of a right hander) at the point of impact. Ben Hogan described this hip movement as a matter of throwing your lead hip around and back against the wall — one of the most useful images in all of golf instruction.
Try it in slow motion. Place your club head along the swing path about 18″-24″ behind the ball (on the inside/out arc). Make sure your lead hand and arm are straightened as they should be in the impact position. Now rotate your hips so the club head moves towards the ball (keeping your hands and arms locked in the previous position).
Notice that when your club head reaches the ball, your hips will be “cleared”, and your lead shoulder will be rotated as well. Your lead arm will be in the correct “power position” with the arm and club shaft forming a more or less straight line down to the ball.
Now pick your club up and swing it more horizontally like a baseball bat. If you have had any baseball training at all, your hips will just naturally lead the swing and your shoulders, arms and “bat” will follow.
In fact trying to make an “all-arms” swing without hip rotation will feel awkward and unsynchronized. Your arms will not be able to follow the momentum that wants to carry them around to a natural finish. This is why golfers who do not “finish” their swing by rotating their lower body will often snap the club back to the starting position.
The basic principle here is one taught by golf teachers since teachers first started analyzing the swing: upper body follows lower body. Coming to a better appreciation of this principle can only have a positive impact on your golf swing.