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This is really nitty-gritty stuff, but it is crucial to understanding why pitchers are so unpredictable, and it bears strongly on the Rockies' 2011 prognosis, so bear with me.
Ubaldo Jimenez looked absolutely unhittable for the first two months of the 2010 season. Through May 31, the day on which he threw the pitch in this photo, his ERA stood at a freakish 0.78. He absolutely dominated with a mix of at least four above-average pitches, including the hardest fastball among starting pitchers in all of baseball.
Beginning in June, though, Jimenez suffered a slow decline. His ERA from June 1 forward was 4.08, and his WHIP leaped from 0.93 to 1.34. What happened?
There were many reasons, of course. Regression was inevitable, so chalk part of it up to the law of averages. Another part can be attributed to the weather, which favors hitters as it warms through June and into the heat of summer.
Part of the problem, though, was within Jimenez's control. He could have been much better simply by consistently extending his arm more during his delivery.
Arm extension is critical in making all of a pitcher's offerings work. It is a critical component of repeatability in mechanics, which dictate control. The tension throughout the arm also ensures that the muscles will whip and twist more eagerly, creating more and better spin. The slight additional length of the levers in the delivery when the arm is fully extended also improve velocity.
Here are maps of Jimenez's release points in three 2010 outings. First, from his no-hitter on April 17:
Next, from a June 23 outing in which he lost to the Red Sox:
And finally, from a rough late-season outing against Arizona:
The pattern is clear: When Jimenez gets full extension to his release point, especially on his curveball and tailing heat, he is untouchable. He struggles only when he gets tired or lazy and allows his release point to wander ever closer to his head, hurting his control and the general nastiness of his great stuff.