Pitching Backward: Sing, Sing, Sing, for the Unsung Affeldt

Many pixels will be burned describing Madison Bumgarner’s historic performance in the World Series. Many will be dedicated to the Giants as a group, and about how they came together as a club despite effectively losing much of the rotation that had carried them to two previous championships. Many will be spent describing the Royals’ unexpected run through October. I suspect that precious few pixels will be earmarked for Jeremy Affeldt, one of the unsung heroes of the Giants’ postseason success. I aim to rectify that.

At 35 years old, Affeldt has already had a long and distinguished career. He’s pitched in the major leagues for 13 seasons and has now won three World Series rings. All told he has pitched in four postseasons, including a losing bid in 2007 with the Rockies. He has thrown 31 innings in the postseason, while posting an ERA of 0.86. Needless to say, that’s much better than his regular season performance.

More impressively, at least from the Giants perspective: He hasn’t given up a run in a postseason appearance since 2010. Affeldt has had 22 consecutive scoreless appearances in the playoffs, one fewer than Mariano Rivera, who needs no superlatives but serves as one when compared against. When Bruce Bochy felt the need to pull starter Tim Hudson in the second inning of last night’s Game Seven, he turned to Affedlt, his bridge to Madison Bumgarner and a World Series title. Affeldt’s success raises many questions, but it’s not difficult to understand why Bochy had so much faith in the lefty.

Since 2007 Affeldt has thrown just four pitches, though that largely overstates his effective repertoire. We can mostly ignore the splitter because he has thrown it only 10 percent of the time since 2007, and his usage of it hasn’t really changed significantly over time. What is more interesting is how Affeldt has traded his four-seam fastball for a sinker over time, as shown in the chart below:

Using Affeldt’s postseason appearances as benchmarks we can see that his repertoire in 2007 basically included a four-seamer more than 50 percent of the time, supported by roughly 37 percent curveballs and 13 percent sinkers and splitters. In that 2007 season Affeldt pitched to a 3.51 ERA (4.17 FIP) but pitched well in five postseason innings, giving up just one earned run.

In 2010, Affeldt’s second full season in the Giants’ organization, he threw more sinkers than four-seamers for the first time. That year was actually Affeldt’s worst as a full-time reliever, as he posted a 4.14 ERA (3.98 FIP) over 50 innings. He saw only four innings during the Giants’ first World Series run, and gave up two runs. Those would be the last times a runner crossed home against him in October.

By 2012 his transition had hit what I’d call a stable point. His sinker usage hovered around 42 percent from 2010 through 2012, while more four-seamers were replaced by curves and splitters. Despite scuffling in 2010, Affeldt wasn’t discouraged, and his evolution produced solid results: a 2.70 ERA (2.73 FIP) for a title-chasing Giants’ squad. In the postseason Affeldt was lethal, posting 10 scoreless innings, during which he struck out more than 8.5 batters per nine innings and walked fewer than 2.7.

This season Affeldt’s tweaked repertoire reached critical mass. The four-seam fastball has been effectively eliminated from his toolbox, and he’s throwing roughly two-thirds sinkers at this point. That’s supported by a mix of curveballs and splitters at a roughly 3:1 ratio. In 55 innings he posted an ERA of 2.28 with a FIP of 2.86, which suggests he hasn’t just been lucky. He threw 12 scoreless innings in October, with more scoreless outings than any other pitcher in the postseason this year.

Why the shift from four-seam fastball to sinker? Both pitches have roughly the same velocity at 92 mph, so it’s not about throwing harder. One key difference is movement, as the sinker has around six inches more arm-side run than the four-seam fastball did, as you can see below:

This results in a completely different zone profile for Affeldt’s fastball, which can have a big impact on how both lefties and righties approach their plate appearances. Over his career, the four-seam fastball worked toward the lower left portion of the zone, whereas the sinker has worked toward the lower right portion of the zone. The differences between the two are clear in the zone profiles below (click to make bigger):

The left chart showcases how Affeldt used his four-seam, while the right shows the sinker. It’s clear the differences, though the importance might not be as obvious at first blush. Since Affeldt is primarily a fastball-curve type pitcher, the sinker provides a different look to opposing hitters. Affeldt’s overhand curve breaks from the top right of the zone to the bottom left. That means that many of his pitches would end up in the same portions of the zone, allowing hitters to eliminate entire sections of the zone in plate appearances against the left-handed reliever. The sinker provides a different look, and means opposing hitters can’t simply sit on pitches over the left side of the plate.

Affeldt has reinvented himself in his late career by simply tweaking which fastball he threw the majority of the time. Affeldt’s late-career renaissance is a function of this reinvention. His postseason success–well, a lot of that is likely luck. Sometimes though, it’s better to be lucky than good. In Affeldt's case, it's been best to be lucky and good.