In contrast, Roger keeps his arm straight and continues to move his hand backward and upward tracing a circular path. His arm stays straight longer and the tip of the racket doesn't point nearly as far to his right. When he begins to bend his elbow, the motion still moves on a curve upward. As noted, the only current player with a more circular path is Philippoussis, similar to the great John McEnroe in a previous generation.
Someone with a greater knowledge of joint structure will eventually explain this fully, but for whatever exact physiological reasons, the more circular paths are much more likely to result in a good racket drop for the vast majority of players. It has to do with range of motion in the shoulder joint. Players like Sampras and Roddick complete the backswing mainly by rotating the upper arm backwards in the shoulder joint, what is called external rotation. This is what creates that incredible racket drop position that is so characteristic of their motions.
Another look at the three examples of racket drop: Sampras, Roddick and Federer.
The interesting thing about Roger is that his drop isn't as deep as either Andy or Pete. You might argue that this is actually a function of the longer backswing and that he should shorten his motion. But I think it's the opposite. What I see is that Roger's shoulder doesn't seem to be quite as superhumanly flexible. That's why I think the longer more circular wind up probably maximizes his racket drop.
You can see the difference by looking at the angle of the forearm to the court at the deepest point in the drop. Roger's forearm is basically parallel to the court. Sampras and Roddick go further. By rotating the upper arm back a little further in the shoulder joint, they drop the hand a little further down. You can see the line of the forearm for these two actually drops down a little below parallel to the court. This is reflected in the actual location of the racket head which is lower and closer to the court. If Roger's armcould rotate a little further back, you would probably see his positions match Pete and Andy more closely.
Now don't get me wrong, Roger has a great racket drop. The rest of us should be lucky enough to make the same position. But it's not quite as deep as Andy or Pete. Because his shoulder probably isn't quite as flexible, the more circular windup probably helps him maximize this position in his motion. And if it's true for Roger, how much more true is it for the average player?
The truth is very few players can achieve the maximum racket drop with an elbow position that is horizontal or lower. Even many pro players. The problem with the abbreviated motions is that they put a premium of this component of the backswing to achieve the racket drop. Yes, it would be great if most players could rotate the arm further backwards at the full drop. That could only mean more racket acceleration in the motion upward to the ball. And it's something you can probably improve by various techniques designed to increase your shoulder flexibility--strength training, stretching, deep tissue massage, etc.
The line of the forearm indicates the amount of external rotation.
Philipoussis displays a great example of form despite--or because of--the backswing.
But the point is to develop the best possible racket position given whatever natural ability you have. The alignment of the racket on the right side of the body with the tip pointing basically down at the pro drop position is critical. It's better to do this with a higher elbow position than not to do it at all. Otherwise you end up with the racket at a diagonal across your back when it starts to the ball. My experience shows me that the path more directly upward is absolutely critical to maximize your power and spin potential. Again, it would be great to have a deeper racket drop with the shoulder rotating even further backwards. But this racket alignment with the racket tip pointing basically down seems to maximize the effect of whatever natural rotation you really have.