2019 Rotation: Presenting the Case for Brad Peacock

In a continuation of an ongoing series, TCB is proposing a few different internal options to fill the likely void(s) in the Houston Astros starting rotation as we turn to 2019. Earlier this month, Spencer got the debate rolling with his piece on Josh James, and last week HebrewHammah continued the discussion in his argument for Collin McHugh to resume his starting duties. Today, I’ll be presenting the case for another member of the Astros bullpen to rejoin the rotation: Brad Peacock.

The story of 2018 Peacock is both interesting and befuddling, but let’s rewind a little bit first. Peacock was arguably the most reliable component of the Astros entire pitching staff (pre-Verlander) in 2017, and no one really thought he’d even make the team out of Spring Training. Although he had mixed success in that year’s postseason, he was huge for the Astros in Game 3 of the World Series.

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But after the Astros traded for Gerrit Cole last offseason, Houston’s stacked starting rotation relegated Peacock to a bullpen role heading into 2018. Peacock’s transition to the bullpen didn’t seem as much a demotion as a luxury, and one I think excited both the organization and fans alike. Although Peacock didn’t have a bad season in 2018, it unfortunately didn’t transpire the way many expected. He wasn’t even included as a member of the postseason roster for the Astros in either series. Let’s take a deeper look at his season and see if we can uncover what happened.

The interesting part of Peacock’s 2018 is that he was better in many regards this year. Peacock’s K/9 (13.29), BB/9 (2.77), and K-BB% (27.9%) were substantially better in 2018 than 2017, when, as a starter, he ranked 16^th in the American League in strikeouts (161). His SIERA was lower this year than it’s ever been in his career, which may not come as a surprise because he was pitching in relief more often than ever. According to FanGraphs, a 0.37 reduction in SIERA is expected—assuming performance remains constant—for a pitcher that moves from the rotation to the bullpen. However, Peacock’s SIERA decreased by 1.36 points in 2018—more than 3.5 times the expected reduction simply by moving to the bullpen. His xFIP-, which is a park and league-adjusted version of FIP with league average set at 100, was 67 in 2018 compared to 85 in 2017. Each point below 100 is one percentage point better than league-average, so Peacock was 33% better than league-average based on his xFIP-.

The befuddling part of Peacock’s 2018 is that it still seemed like his performance declined from the previous year. That may be because Peacock’s improved numbers didn’t really show up in his surface stats. For instance, even though Peacock’s xFIP (2.82) was nearly a run lower in 2018 than 2017 (3.73), his ERA (3.46) was about half-a-run higher than the previous season. But it’s not as though his ERA (or FIP) ballooned to an obscene number; for some reason, it just didn’t really feel like Peacock was better in 2018 either. He gave up a few walkoffs early in the season (at Minnesota and at Cleveland, both in extra innings, stick out in my mind), blew three saves, and had five losses a year after going 13-2. Fair or not, that likely impacted the perception (or at least mine) of Peacock’s performance this season.

Certainly, a few things were different for Peacock in 2018. The most obvious is that he was pretty much a starter for the entirety of 2017. Sure, Peacock only made one start in the 2017 postseason before transitioning to a bullpen role for the remainder of the playoffs (in which he was pretty good, for the most part), but it’s a pretty big difference going from starter to reliever for a full season, especially mentally. To his credit, there was never any complaint from Peacock about his role. There are differences in the physical aspect as well. He’s throwing fewer pitches per outing out of the ‘pen, so he can throw harder and with more intensity on each pitch as opposed to having to leave something in the tank when starting. Thus, it makes sense that some of Peacock’s numbers should improve as a result of moving him to the bullpen.

Probably a bigger factor in Peacock’s perceived decline than his role change, however, was the rate at which he surrendered the longball. Even though his LOB% improved, his HR/9 jumped from 19.0% to 27.9% and his HR/FB more than doubled—all the way up to 18.0%. Shockingly, he gave up more home runs this year (11) than last year (10), despite throwing twice as many innings in 2017. His HR/9 rate in 2018 was actually in line with his career numbers, with the exception of 2017, which is disconcerting.

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Peacock clearly gave up more hard contact this season, but why, and should we expect that trend to continue?

One thing I noticed was a pretty big difference in the average launch angle for opposing batters against Peacock. Below you will see his average launch angle allowed for both 2017 and 2018.

As you can see, there’s a pretty big difference on the launch angle for all pitches, but particularly those up and out of the zone. Crazy thing is, up in the zone is where Peacock got a lot more swing-and-misses as well in 2018, as you can see below.

So, although Peacock did a better job of limiting contact and baserunners in 2018, hitters did a better job of elevating the ball. What that is attributable to, I don’t know. Peacock altered the grip on his slider midseason during the 2016 All-Star Break after a discussion with a teammate, and his results really took off afterward. His slider usage wasn’t very different from 2017 to 2018, though he did throw his four-seam fastball more often this year and his curveball less. Is Peacock more of a finesse pitcher, the type which needs to pitch on schedule and throw more innings to get the most out of him? Maybe. I’m sure the league made an adjustment against him, but it’s not like we saw decline from Peacock in every category, or even many of them. He was a better pitcher in at least a few regards in 2018, and that was after a pretty fabulous 2017.

So, I don’t really have a confident answer about whether Peacock should rejoin the rotation in 2019. I do want Peacock to be a starter next year because there will likely be a need, he is just one season removed from great success in that role, and his slow, winding path to the Majors makes it easy to root for him. What are your thoughts on his potential return to the Astros’ rotation in 2019? Should we let the Peacock fly again?