During his struggles last April, Jake Peavy's slider was to blame. But as he improved, so did his that pitch.
April was a cruel month to Peavy in 2010, as the right-hander posted a 5.79 FIP. Behind that poor start was 20 walks in 28.2 innings pitched, and behind that high walk rate was a lack of success with his slider. Opponents swung at 50 percent of Peavy's sliders and whiffed at just 6.7 percent of them in the season's first month—both low for a go-to pitch.
So it's not surprising that Peavy's improvements in May and June coincided with better success with his slider. In May, Peavy had a 3.79 FIP—although he was incredibly unlucky, with a 5.79 ERA. But opponents swung at 56.8 percent of Peavy's sliders with a 21.1 percent whiff rate, so while the results weren't much better, it's not surprising that Peavy actually pitched better.
June represented Peavy's best stretch of his injury-shortened 2010, as he had a 2.94 FIP and 1.75 ERA for the month. While his slider whiff rate regressed to 13.7 percent, his opponents' swing percentage remained essentially the same at 56.2 percent. And while luck certainly played a factor in Peavy's success—opponents had a .230 BABIP and Peavy stranded about 85 percent of baserunners—his above-average slider was a significant factor in his success as well.
Looking at the entirety of Peavy's sliders from last year, an interesting trend emerges: Peavy didn't throw his best pitch as much to left-handers.
Heat maps, as always, via Fangraphs.
Given that Peavy's slider was rated as his best pitch last season (technically, his curveball rated better, but he only threw it 5 percent of the time), I expected to find that Peavy was worse against left-handers than righties in 2010. But that wasn't the case—against lefties, Peavy had a 3.69 FIP; against righties he had a 4.31 FIP.
The pitch that supplanted Peavy's slider against left-handers was his cutter, which rated as about an average pitch in 2010. In fact, Peavy threw more cutters—and changeups—in general last season.
It's interesting that Peavy has thrown a fewer percentage of sliders over the last few years as compared to his heyday with San Diego. Whether it's a calculated strategy change remains to be seen—we haven't seen a large enough sample size over the last two seasons to determine that. But heading into 2011, the percentage of sliders thrown by Peavy certainly is something to keep an eye on. It's his best pitch, and if he throws it less he'll have to be more effective with his other pitches.
This is all contingent, of course, on Peavy being healthy—which his hardly a guarantee.