Making Sense of Wade Miley

Excluding Brandon Beachy, who will be sidelined for the remainder of the season due to Tommy John surgery, left-hander Wade Miley has the second-best ERA in all of baseball.

The same Wade Miley who compiled a forgettable 5.08 FIP in his 40-inning cup of coffee with the big league club last season. The same Wade Miley who failed to make our Top 15 D-Backs prospects prior to the season. The same Wade Miley who began the season in the bullpen and didn’t make his first start until April 23 against Philadelphia.

And yet, the 25-year-old Louisiana native boasts a 2.19 ERA and 2.88 FIP, including eight innings of one-run baseball against the Chicago Cubs on Sunday evening. His +2.5 WAR is higher than pitchers more traditionally thought of as aces, such as Cliff Lee, Cole Hamels, Clayton Kershaw, and Felix Hernandez. In his first full season in the big leagues, he is not only a leading candidate for Rookie of the Year, but he also possesses an extreme outside chance to walk away with the NL Cy Young, if his stellar performance continues.

That’s really the question, though. Can Wade Miley continue his unexpected dominance?

His 3.64 xFIP and 3.54 SIERA suggest that his numbers are a bit misleading and due for regression. It seems unlikely that he will be able to sustain a 0.40 HR/9 home run rate and a 4.8% HR/FB ratio, given the home ballpark. Chase Field has the second-highest home run factor (1.832) in all of Major League Baseball to this point in the season, ranking just behind Miller Park. Without extreme ground ball tendencies in homer-friendly Chase Field, one can reasonably assume that the second half of the season will yield more home runs allowed by the southpaw, and thus, more overall runs.

Miley also generates fewer strikeouts and swinging strikes than the average major league pitcher, which should limit his effectiveness down the road. His low strikeout rate is partially due to his heavy reliance on his fastball. Only Bartolo Colon, Justin Masterson, and Lucas Harrell throw their fastball more often than Miley. Of course, a heavy reliance on a fastball does not necessarily correlate to lower swinging-strike rates, but for Miley, it does. He only generates whiffs on 5.0% of his four-seam fastballs and 6.7% of his two-seam fastballs. Despite the plethora of fastballs featured per game, his best pitch is actually his slider, which he throws much harder than he did last season and generates a swing-and-miss 12.4% of the time. It will be interesting to see if he relies more on that pitch in the second half.

When it comes down to it, the former supplemental first round pick in 2008 has found success through limiting walks, limiting home runs, and a friendly .255 BABIP. The home runs should be expected to increase as the season progresses. The BABIP, however, may not rise as much as one would think. The Diamondbacks have the second-best defense in the National League this year, combining for a +16.2 UZR thus far. Miley features a ground ball rate slightly above average at 49.1%, and a quality defense that features John McDonald and Aaron Hill up the middle should help limit some ground ball base hits, while the stellar outfield defense (even without Gerardo Parra) should rob its fair share of base hits, as well.

This isn’t a case where we simply look at the .255 BABIP and call for regression. The Diamondbacks’ defense and Miley’s above-average command should keep the BABIP better than average. Still, the FIP, xFIP, and SIERA numbers all suggest Miley will not be able to maintain his current performance level of a low-2.00 ERA. They certainly suggest an above-average major league pitcher, just not the second-best active pitcher in the league this season. Given the below-average strikeout rate and unsustainable home run rate — especially in Chase Field — it seems acceptable to expect regression in the second half.

Just how much regression will likely be tied to just how many home runs are given up and how well big league hitters can adjust to Miley, now that the proverbial book has been written on him since the majority of the National League has seen him at least once.