Why is the proper club path inside out?
We have been discussing swing plane and preventing the "over the top plane" or "outside in path." The proper path is inside out. Now let's talk about why it's like this...not just because I said or because that is what Tiger does.
A popular golf drill is the "three tee reroute drill." Below is an image that shows the straight takeaway (1), the inside to out route back to the ball (2), and the extension (3). I'm focusing on the first two.
The question is asked "If I take it away on one path and return it on a different path, isn't that changing my swing plane to swing on two different planes?" The answer is no.
First understand the difference between the two – "plane" is 3-D, up in the air, and "Path" is 1-D, it is like a paint brush stroke along the ground.
The "path" is different, but the "plane" remains the same...sounds like geometry, but is really simple.
A practice swing thought:
Place a club on the ground perpendicular to the target line (or parallel to your shoulder line at the top of the swing). Don't hit the ball. Just stop at the top and then swing along that club to start the downswing. Natural shoulder rotation will bring the club back to impact, but this time on plane and with the proper path.
Take a look at Charles Howell III's shoulders at address. They are parallel to the line to the target. Therefore, when the shoulders begin to turn around the spine on the takeaway, the club head goes straight back for a foot or so (toward tee #1.)
But when the swing is at the top, the shoulders are in a completely different starting place. His shoulders are at a 90° angle or perpendicular to the line going to the target. Therefore, when he first begins the downswing, his shoulders will rotate around his spine moving inside out to begin. As it continues, the club moves from behind the back, then to his side, then to impact. Like a tetherball around a pole, the golf club never is moving in a straight line, thus the inside out path into impact (along tee#2.)