Jake Arrieta allowed 17 unearned runs in 2018, the most in all of baseball and at least four more than every starting pitcher in the majors except Francisco Liriano.
That should change in 2019, with an improved Phillies defense. The Phillies will be better defensively at two positions, if not more, this upcoming season. Jean Segura is a better shortstop than anyone who played there for the Phillies last season, and Andrew McCutchen is obviously a much better corner outfielder than Rhys Hoskins, who moves back to first base.
It felt like Arrieta was worse than he was in his first year as a Phillie, because of both the unearned runs and his lack of reliability during the Phillies' coldest stretch of the season - which just so happened to be the stretch run. Over his last nine starts of the season, Arrieta had a 6.35 ERA and the Phillies went 2-7.
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When you look at Arrieta's season in totality, it wasn't that bad. He had three very good months and three bad months. More was expected, but Arrieta is not the Cy Young candidate of 2015 and the Phillies didn't sign him to be that guy. They signed him because he lingered in free agency until the second week of March and because he was a clear rotation upgrade over what the Phils had.
Arrieta is a bounce-back candidate in 2019, and with the Phils' improved defense and perhaps better run support (which has an immeasurable psychological impact on a pitcher, the same way a 10-point lead in the NFL affects how a defense plays), we could see an ERA closer to 3.50 than his 3.96 this past season.
Arrieta did lead the National League with a groundball rate of 51.6 percent. Aaron Nola ranked second in the NL and Nick Pivetta was 10th, one spot ahead of Jacob deGrom. It's a meaningful metric. Even more meaningful is Arrieta's 27.7 percent rate of hard contact, which was fourth-best in MLB behind only Zack Wheeler, Nola and deGrom. It didn't mean a ton of success for Arrieta in 2018, but it's a better future indicator than his ERA.
As far as all the ground balls, consider that the league average batting average on grounders last season was .243. Against the Phillies, it was .255. That's a difference of 17 or 18 hits over a full season. It all adds up.
And if the Phillies do land Manny Machado to play third base, that would be three important defensive positions they upgraded. It would make their pitchers look better, and it should theoretically get guys like Pivetta and Arrieta closer to the ERAs their peripheral numbers match up with.
There has been a ton of focus this offseason on the Phillies' improving their rotation, and they do still need at least one more starter even if it's for depth. But improvement can also come from within.
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