Tiger at the top of his backswing

Note that at the top of his backswing, Tiger's shoulders have turned more than 90 degrees, whereas his hips have not turned much at all.  That's what we mean by torso spring.  By spey casting with right foot forward when his right hand is up, Gordon Armstrong uses this same wound-torso (wound up spring) position from which to deliver extra power into his forward stroke.

Tiger Woods' Golf Swing -- Slow Motion (4 MB)
If you would like to watch the complete slow-motion video of Tiger's swing, click on the movie icon  (For fastest download, save this video to your computer before opening.  Do this by right clicking on the icon, and "Save Target As ...".)