Bob Toski and Jim Flick in ‘How To Become A Complete Golfer':
At the top of Bob Toski's backswing, his weight is well on his right side and his lower body is in position to lead and support the forward swing. Toski's left knee initiates the forward swing with a lateral movement, while the right leg remains stable. Note how the gap between the right leg and left knee widens, indicating that the lower body movement is coming from the left., not the right. The left knee and hips then begin to turn, pulling the right leg along . . .
A good player actually has a ‘down-drive' with his legs, the knees flexing and moving slightly downward as they shift to toward the target. Bryon Nelson's swing provides a classic example of this, as do the swings of Tom Watson and Tom Weiskopf among the current stars. This down-drive with the knees forces the head to stay down and back where you want it. The left knee is flexed at impact and the right heel stays relatively close to the ground.
The sequence of Toski shows quite a large gap between the knees. As Bertholy indicates, it does not look quite pulchritudinous. I remember having seen an article featuring Sam Snead showing a very large gap between his knees, ugly looking - I think it was referred to as a ‘split-knee' position.
However, to my delight, the opposite idea is taught with equal eloquence.
. One is instructed to try to close the gap between the knees early in the downswing. One teacher with comes to mind is Michael McTeigue, but I think David Leadbetter teaches it also. One is instructed to imagine have cymbals attached to the knees and to clash them together in the down swing.
Hence, in the end, it comes down to a choice between looking, for a floating moment, rather ugly or giving in to one's musical instincts.
mandrin
