The Prevailing Wisdom:
Pull shots result from a fast left side. Slow down your left hip and you'll stop pulling the ball to the left.
Why It's Misleading:
Because it doesn't jibe with physics and the conservation of momentum. Think about why a whip cracks or why you should always wear your seatbelt while driving your car. When one part of a moving system stops, another part picks up the motion. During your swing, if you slow down your left hip rotation, your right side will hit the gas and shoot past, ruining your sequence and creating a pull. The Mistake
Your shots start way left of target If you're hitting the ball left, you're usually making pretty good contact. Nevertheless, your pulls have to stop.
You probably blame your upper body or your hands for causing the pull. But you should also consider your hips. Like most golfers, you have about half the hip rotation of a Tour pro because (1) you don't turn enough, and (2) you begin your downswing with your shoulders. These hip turn errors force your club across your target line (an over-the-top swing). Your shots start left of target then fade, hook or go straight depending on your face angle at impact.
What You Should Do
Conserve your fast point Understand that maximum power and accuracy result from your right side whirling toward the target, but only after your arms drop the clubhead into position from the top. In other words, save the "fast point" of your downswing for impact.
To do this, rotate your left hip toward the target as you shift your weight to your front foot. Leading your downswing with your left hip produces the correct sequence: left hip, left shoulder, arms and then your clubhead.
The Old (And Flawed) Fix
Keep your back pointing toward the target on the downswing The logic here is that by keeping your back toward the target you'll slow down your left side and give your right side time to swing your club from the insideout. This sounds accurate enough, but any move that slows down any facet of your swing is a poison. If you try to slow down your left side, you'll under-rotate your left hip. Your shoulders and arms then have no choice but to flip across your body and pull the ball to the left. The more you hold your left side, the worse your pull.
The Modern Fix: Speed up your hip turn
Rotate your left hip sooner and more aggressively from the top of your swing. This positions your clubhead behind your shoulders where it belongs. It also ensures that your left shoulder won't catch your left hip until well after impact. As soon as your weight hits your front foot, all you have to do is keep moving every thing that's moving. This is how you produce the sequence where your left hip is chased by your left shoulder, your left shoulder is chased by your hands, and your hands are chased by your clubhead.
Drill Instructor: Avoid a collision
To see if your sequence is solid, and that you're correctly chasing one body part with another, grab a 7- and an 8-iron and hold one club in each hand. Get into your address position with the clubs about two inches from each other. Swing slowly to the top of your swing and then through. If you conserved your fast point and produced the correct downswing sequence, then the clubs will not collide. If the club in your right hand catches the club in your left, then you slowed down your left side. Once you're able to swing without the heads or the shafts colliding, speed up your motion until you reach full power. To swing faster, speed up your midsection. This applies to this drill and for every swing with any club.