Hall of Fame

I notice that the Adidas stripes on the right sleeve disappear between the previous frame and this one, suggesting that ESR (external shoulder rotation) plays a big part in squaring up the racket face in this situation. Seems to me that ESR is a screwy description. With the humerus or upper arm being the axis for said rotation, and the shoulder being a "joint" rather than a rod or an axis, might it not be better to name this rotation something else - like something related to the upper arm bone??

While I'm at it, how come we don't hear more about the racket face changing so much this late in slice strokes? This Flickr "album" is loaded with such examples.