If you'll allow, I'd like to stray from the "op/ed" nature of this column for a moment to cover the "positions" or "Ps" in the golf swing. For many this will be review, but many will hopefully learn about these "positions" in the golf swing.
Update 2012-02-23: In the 5 Simple Keys® (5SK) world we've chosen to call these the alignments in the golf swing, as we wish to put less emphasis on "positions" and view them more as checkpoints at which some measurements might be taken.
I'll choose Charlie Wi for many of the pictures simply for consistency's sake and because I know this particular swing illustrates something at A6.
A1 - Address
Very simple one to understand, as A1 is the setup or address position. You can judge things like posture and overall setup, ball position, handle location (too close to the thighs, leaning back or forward too much), the hang of the arms, weight location (toes/heels as well as forward/back).
A2 - Shaft Horizontal (Backswing)
This position allows you to look at how quickly the shoulders are turning, how quickly the wrists are hinging/cocking, how much the wrists and forearms are rolling, whether the head is translating or staying relatively stable, how much the shoulders have turned, etc. This is one of the somewhat "looser" positions because the wrist cock will determine the location of A2. For example, Charlie Wi hits a fairly normal A2 position (albeit one with a lot of depth):
But Rickie Fowler's A2 looks funny because he doesn't roll his forearms at all in the start of the backswing:
Steve Stricker sets his wrists later, so the shaft "ascends" more slowly and "arrives" at A2 a little "late."
Late wrist sets will tend to look like the club has been taken more inside or under than it really has, and early wrist sets will tend to look the opposite.
A3 - Lead Arm Horizontal (Backswing)
When the lead arm is parallel we can check the wrist cock (typically around 90 degrees), we can check the shaft plane and the plane of the hands (where are they coming out of the body - base of the bicep? Top of the shoulder? Mid-way?), we can check relative shoulder turn (some people stop turning here, some haven't turned enough because they've just swung their arms back). We can check the head, the shoulder pitch becomes evident down the line, and more.
Note that Rickie's backswing is a product not of quickly cocking the wrists but of allowing very little rotation of the forearms or wrists ("accumulator #3" in TGM). His left arm to shaft measurement at A3 is only 107 degrees).
Of course, Steve Stricker's is even more:
A4 - Top of the Backswing
Wherever this player reaches the top of the backswing, that's A4. Note that a shaft isn't necessarily "laid off" if it points left of the target before the shaft reaches horizontal, nor is it surely "across the line" if it is pointing right but past parallel. Many things can be checked at A4 - wrist conditions, shoulder tilt, any translation off the ball, plane, right elbow flex, left arm position, weight/pressure/CG location, etc.
A5 - Lead Arm Horizontal (Downswing)
This position can tell us many things as it's early enough in the downswing that a player can still make changes much more easily to affect A6 and A7. How far "in" is the left arm? What's the shaft done based on the wrist conditions? How's the right elbow working - towards the belt buckle or staying behind the rib cage? Have the hips begun going forwards? Has the head started tipping back? What's the plane of the shaft like?
Note that in Rickie Fowler's case, "lag" appears excessive but it's an optical illusion. He's simply "laid the shaft down" so much that the face-on view is not a good indicator of lag.
See the blue lines on the left? Imagine they represented his left arm and clubshaft. Imagine he rolled his left forearm and wrist enough to lay the shaft down that much. Look at how much "lag" it would appear he has from the face-on view! In reality, "lag" should be measured from perpendicular to the plane containing the three points: left shoulder, left wrist, clubhead. It might surprise you to know that Rickie doesn't have a ton more lag than good ol' Steve Stricker, but the camera position and the "laying the shaft down" throws you off:
A6 - Shaft Horizontal (Downswing)
A key position. There are a lot of things you can check here, but one of the keys is where the clubhead is relative to the hands. Charlie is pretty well "on-plane" here:
Note the two lines I've drawn. If your clubhead appears beneath or inside of your hands - the location of the green line - you're quite likely going to send the path of the golf club out to the right. If your clubhead is outside your hands or above the plane like in the right, you're quite likely sending the clubhead path left. The clubhead in the red case is "over the top" of the hands plane - one of a few definitions for that term ("over the top").
Though A6 is highly sensitive to camera position, it's clear that Steve Stricker is going to "hit out" at this ball, while Rickie Fowler - despite "laying the shaft down" heavily from P3.5 to P5 - is coming down pretty well on-plane.
Skipping ahead a little bit, I think this picture will make a little sense to people. I've traced the clubhead in both Steve Stricker's swing and Charlie Wi's (Rickie's is similar to Charlie's). As you can see, the tangential line at the bottom of the swing arc in Steve Stricker's swing - called the "base plane line" or "base line" - is pointed well to the right. If you imagine creating a plane on the arrows, the base of it would rest along the blue arrow. Charlie's (and Rickie's) plane is much more "at the target" than Steve's.
Steve Stricker plays a ball that pushes and draws a little, and catches the ball just in front of of low point to help the clubhead go a little left to take some of the draw curve off of his golf ball.
Final note on P6: good golfers tend - nine indeces on downward (with increasing frequency) to get "under" plane or "stuck" (hello, Tiger Woods!), while poor golfers tend to be "over."
A7 - Impact
Things to look for here are fairly obvious: clean contact, clubhead traveling in which direction (ideally +/- a few degrees), handle leaning forward an appropriate amount (0 to 10 degrees, rarely more; less with the longer clubs, more with the shorter ones), etc.
A8 - Shaft Horizontal to the Ground on Follow-Through
A9 - Lead Arm Horizontal to the Ground on Follow-Through
In virtually every golf swing, the shaft is horizontal to the ground before the lead arm, but the two are sometimes very closely timed. These images are from before A8 and A9, but honestly, A8, A9, and A10 are almost never used in discussing the golf swing because they're simply an indicator of what's come before. They are however quite useful in instruction, as a student modeling a position at A8 or A9 will introduce changes to his motion prior to A7 which will have (if the instruction is correct) positive results.