There's a lot going on in the split second it takes for the club to move from behind your head down to the ball. So much that you really can't pinpoint any one element as being the most important. When my coach, Cameron McCormick, and I are fine-tuning my swing, we like to make sure I'm moving through certain positions during the downswing. Here's what we see and like in this photo from the PGA Championship last summer at Whistling Straits. —With Ron Kaspriske
1) LEFT HIP
From the start of the downswing, my left hip is turning behind my torso. It's most noticeable at impact, and it signifies that my lower-body rotation is leading the way to the ball. What you don't want to see is the lead shoulder directly above the lead hip as you swing down. That's a classic sign that the club is coming from outside the target line—and the ball's going to slice.
Shifting toward the target on the downswing is critical, but not to be overlooked is what my feet reveal here. The toes of my left foot have rolled off the ground, proving that my weight has moved into my left heel. That allows me to straighten my lead leg so I can pivot my body and swing around that leg like a post. On the other side, the heel of my right foot is off the ground. That shows I'm pushing through for extra leverage into the ball.
My hips have really rotated through, but you can see here that the upper half of my body is not going as hard—it's basically facing the ball. Also, my right shoulder is still substantially lower than my left. Cam says these positions create a conduit for moving the energy I've created during the downswing out to the clubhead for maximum speed.
There are two things to notice regarding my head position. The first is, despite a lot of lower-body thrust, my head looks to be in the position it would be at address. If it didn't remain pretty stable during the swing, center-face contact would be a serious challenge. The second thing is, I appear to be looking at the ground behind the clubhead. This proves I'm "staying behind the ball," as teachers say. It helps me square the clubface at impact and sling the club out to the ball.
This photo is a milli-second after impact, but the orientation of the club suggests it's moving level to the ground or slightly upward. With a driver, that's what you want to maximize your launch angle and carry distance. You also can see the clubface is very solid—still looking at the ball. I remember this drive ended up in the fairway, Position A.
Jordan Spieth writes instruction articles only for Golf Digest.