In the winter of 2003-2004 I attended a SABR meeting in Rhode Island. Former Red Sox manager Joe Morgan spoke. One audience member brought up the Pedro Martinez melt-down in the ALCS, and Morgan provided a very good explanation of why Grady Little should have removed the ace from the game. Joe pointed out that Pedro lost his change up due to fatigue. At that point in the game, he was throwing nothing but fastballs. Morgan understood that the change was Pedro's out pitch. When he lost that, he was just another pitcher.
Jon Lester of the Red Sox starts against the Yankees tonight on long rest, last pitching on May 30th. He pitched poorly during a streak of five games, and the Red Sox felt he needed a little extra time off to get back to normal. That makes sense, since his change up was at fault.
Through May 3rd of 2011, Lester threw his change up for strikes (click graphic for a larger image).
Lester threw the change up for strikes. Batters hit .154 against the pitch with no walks for a .179 wOBA. Note two, the nice, tight target on the spin graphic. Lester threw the pitch with a consistent spin.
Since May 10th, however, the pitch missed:
The highest density of change ups lies outside the strike zone. In addition, note the spin density looks more like a weeble than a ball. He's not throwing the pitch as consistently as he did early in the season in addition to missing the strike zone. That adds up to a .353 BA against the pitch with a .450 OBP, good for a .395 wOBA.
The Red Sox did the right thing by resting their ace. Why he should be worn down so early in the season is another matter. Boston fans should hope rest is enough to cure what ails Jon.