"1. Since the scapular complex includes the shoulder socket, pinching the shoulder blades helps to maintain humeral alignment in the glenoid during rotation (both internal and external). Having the elbows moving behind the acromial line without pinching the shoulder blades causes misalignment in the glenoid and thus the risk of injury to tissues therein."
But why do it at all? It is unlikely to have little in the way of significant benefit.
"2. I disagree with your statement about Clemens getting into a "good fielding position" as evidenced by the pic of his front glove. Still images CANNOT portray what goes on in a dynamic motion such as pitching. If you review video of him pitching, you'll see that his glove actually goes very far behind him during the follow through."
You're right. He starts off in a good fielding position with his glove at his pec, then gets into a poor fielding position with his glove behind his back, and then finishes in a mediocre fielding position with his glove more to the front but far from the ideal.
"3. Getting into a "good fielding position". If a pitcher attempts to get into a specific fielding position, typically described as facing the plate, with the hands positioned as an infielder would, he is compromising what he's on the mound to do, pitch. Pitchers need to pitch, completely, in the first instance. Any fielding that they may be able to do after that is a bonus. It depends on the location of the hit. Behind him, forget about it. To his glove side, maybe. Also, I'd rather him sideways, with the glove near his chest (not as Clemens does it) for the sake of protection. Facing the hit from such a close distance is treacherous, no matter what position your glove is in."
I kind of agree. I think the real key is that the pitcher is balanced and in a good position to react to the ball. What I mostly don't like is when people finish completely off balance.
"4. Reverse forearm bounce. Firstly, Marshall's comments need to be taken in the proper context. They are not always applicable to the "traditional pitching motion" since his own recommended mechanics are so different. The arm action that Clemens, and 99% of MLB pitchers, uses employs a 'bullwhip' overall action (Nyman describes this well). It has a 'loop'. No pronounced "bounce"."
I completely disagree. When Dr. Marshall talks about Reverse Pitching Forearm Bounce, he is talking directly about pitchers who use the traditional pitching motion. All traditional pitchers experience it to one degree or another. It is a consequence of having the pitching forearm at or near vertical at the moment the shoulders start to turn. Nyman may describe this as a bullwhip action, but there is a clear and pronouced bounce in every pitcher's motion.
"Video of MLB pitchers shows that the forearm does not lay back and 'bounce'."
I completely disagree. It could be that the frame rate of the video that you are looking at isn't high enough. If the frame rate is high enough, then you can't miss it (which is why I rely in part of still frame analysis).
"The hand takes a path that is curved from the "horizontal W" THROUGH high cocked, back and down RELATIVE TO the elbow which is now moving on a more or less horizontal arc, along a more or less horizontal arc, then smoothly up and forward to release and beyond. This is very difficult to explain in words. I have some very good video of Clemens, Mariano Rivera and John Smoltz which show this very well. Let me know if you want me to email them to you."
I would love to look at this video.