A definite must-read at SI today about a new pitch-tracking system that goes deeper than ever in terms of understanding what happens between the rubber and homeplate.
For example, why does David Robertson have such a high K-rate despite not throwing particularly hard (averaged 92 MPH last year, yet K'ed 10.4/9)? A system called "Trackman" says he gets remarkable extension in his delivery that causes him to release the ball much closer to homeplate than a pitcher with a normal delivery -
Imagine if Robertson moves the pitching rubber 14 inches closer to home plate every time he pitches. That's the kind of advantage he gains over the average pitcher by releasing his fastball with so much extension. The radar gun (and Trackman) clocks Robertson's fastball at an average of 93 mph. But because Robertson shortens the distance between his release point and home plate, his "effective velocity" is 95 mph. It looks like 93 but gets on a hitter like 95 -- thus the illusion of "hop."
That's not the only reason he strikes out so many; his plus curveball and inconsistent command also contribute (i.e, hitters never feel too comfortable knowing he'll throw strikes), but you get the idea.
They also measured the spin rate of cureballs and found that the more they spun, the more effective they were (I know, big surprise). Two Yankee pitchers qualified among the top 10 in curveball RPM: Alfredo Aceves and Ivan Nova. Strange to not see A.J. Burnett, but you should realize that these readings have a small-sample size warning: they only come from one ballpark and only span one season. But obviously, they longer they study this, the better the results will be.
Overall, the greater the pitcher's extension, the better the K rate and lower the ERA, and the same for spin rates on curveballs. Essentially, common sense type-stuff, but having it in hard data may motivate changes in pitching philosophy and the reliance on radar guns to evaluate pitchers.