Can you post a link to a face-on view swing video of Anthony Kim's swing, which demonstrates that his head moves back 6"? I can only find DTL views on U-tube.
Unfortunately, that's not a perfect face-on view. I have never seen Anthony Kim's head move back inordinately in any of his U-tube swings. However, I need a perfect face-on view to make accurate measurements of his head movement using a swing analyser program.
Go to the you tube I listed and put your mouse pointer on the right side of his head and watch how much his head moves. If I can see it you can.
If you put your mouse pointer on the tree...you will also see the tree move significantly...that camera is being hand held and is moving around pretty good...not the best footage for monitoring/measuring Kim's head movement.
I don't dispute that his head moves slightly to the right, but that happens very frequently in many professional golfers. I am not sure that his degree of head movement is unusually large.
Here are photos showing the movement of the head in two golfers. The red lines were placed alongside the head at address. The blue dot represents the upper swing center (midway between the shoulder sockets).
Linear Mode
