Very nice find here, thanks for the ref.
Nice Pic here of what we call stalking-
Especially the 1st one.
Stan does a good job of course, but few things to notice,
I'm not a grip zealot, but is it a sw grip? Many say Eastern.
Someone got the pics out of sequence right? for a reason?
Where he says "Federer is turning his shoulders as he’s moving to the ball.
Notice how his left hand is on the racquet even though he’s well into his preparation.
This forces him to turn his shoulders"
This is not just exactly right.
The shoulders have NOT really turned from the body, or done much prep by coiling.
At that point he is really still just running to intercept the ball with everything pointing
the way he is running except his face as it watches the ball come in. His feet, hips,
shoulders are all facing the direction he is running, with the racket still in both hands,
in front of his chest/body/shoulders,(I call stalking) very much like in the ready position.
It's a instant later where he gets some shoulder turn to load and coil his core
for the shot.