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For the first time since early 2020, there is a palpable buzz around the Diamondbacks.
It’s not that the Diamondbacks are favored to win the NL West. Heck, the San Francisco Giants just signed Carlos Correa — the latest addition to a long list of obstacles in what is arguably baseball’s best division. It’s that there is an increasing sense among fans that the next generation of Diamondbacks — including Corbin Carroll, Daulton Varsho, Jake McCarthy, Alek Thomas and a plethora of young pitchers in Drey Jameson, Ryne Nelson and eventually Brandon Pfaadt — could usher in a new era of Diamondbacks baseball that is not only good, but sustainable.
In many respects, that hype is justified. The emerging core of young players might be the best collection of home-grown talent the franchise has ever assembled. Some of them, such as Varsho, have already had multiple productive seasons. Carroll, Jameson and Nelson have only played a month in the big leagues, but have already shown flashes of brilliance.
Moving into 2023, however, every fan ought to come to terms with an undeniable reality about the 2022 Diamondbacks: For many of their key contributors, what the surface level stats said the advanced stats did not buy. Put simply, the Diamondbacks’ 22-win improvement in 2022 appears to have been propped up by a team-wide trend of good luck. And expecting that luck to continue into 2023 might be just as foolish as denying that it existed.
Before we dive in, I’ll explain the two primary stats that we will use for our analysis. The first is weighted on-base average (wOBA) — an all-encompassing offense statistic that reads like an on-base percentage. The league average wOBA in 2022 was .310. The second is expected wOBA (xwOBA), which is the exact same idea but is based on expected batted ball outcomes (using exit velocities, launch angles, etc.) rather than actual batted ball outcomes.
Neither stat is perfect, but in general, if a player’s wOBA and xwOBA are roughly even, that player is probably not over-performing or underperforming significantly. However, a large gap between them — say, more than 15 points or so — is, at minimum, worth investigating.
As a team, the Diamondbacks had a .303 wOBA compared to a .297 xwOBA. A six-point difference is unremarkable for an individual player, but on a team-wide basis, it does suggest some degree of over-performance. That doesn’t mean every Diamondbacks hitter outperformed his expected stats, but it is somewhat troubling when we consider which players, in particular, appear to have over-performed the most.
Once again, when looking at wOBA, think on-base percentage. The difference between a .337 on-base percentage and a .298 on-base percentage, for example, is not insignificant. Over a long period of time, that is the difference between a major-league regular and a depth piece that bounces from one organization to another.
With that in mind, McCarthy’s .298 xwOBA does not necessarily mean his wOBA should been .298 instead of .337, but it’s a big enough difference to warrant investigating. A look at his batted ball data should help us understand why the gap is so large.
In 2022, McCarthy’s average exit velocity of 87.4 MPH was in the 20th percentile — meaning it was better than only 20 percent of other major league hitters. His whiff rate was in the 31st percentile. His walk rate was below average. From a batted ball perspective, there are actually no indicators that McCarthy is an above-average offensive player.
What McCarthy does have is speed — 98th percentile sprint speed, in fact. That speed helps him turn infield rollers into singles and singles into doubles, and essentially means he is bound to outperform other hitters with similar batted ball data. In theory, xwOBA already accounts for that due to a 2019 update that added sprint speed to the xwOBA recipe for certain types of ground balls.
According to one study, though, that update did not entirely mitigate the problem. Based on data from 2015-19, the study found that players with a sprint speed of 29 feet per second or higher (McCarthy’s was 30.1 in 2022) still outperform their xwOBA by an average of 12 points.
That is significant, but still not enough to explain the 39-point disparity between McCarthy’s wOBA and xwOBA. To be fair, McCarthy only had 354 plate appearances in 2022, which really is too small a sample to draw any firm conclusions. What we can say about McCarthy is that, despite his impressive breakout in the second half of 2022, he still has a lot to prove. And fans should at least consider the possibility that his underlying offensive ability is much closer to league average than his lofty 2022 numbers would suggest.
Varsho and Rojas had less extreme disparities between their wOBA and xwOBA in 2022, but a look at the batted ball data still raises some red flags. Varsho, in particular, had an above-average strikeout rate, a below-average walk rate and a 25th-percentile average exit velocity. His expected batting average (xBA) – another Baseball Savant stat that is exactly what it sounds like — came in quite low at .214 . Again, Varsho has above-average sprint speed, which means that a small difference between his wOBA and xwOBA is unremarkable. However, his 25-point disparity is too large to explain by that alone.
As for Carroll, his 65-point difference between wOBA and xwOBA is hard to ignore. Frankly, 115 plate appearances are not nearly enough to put much stock in his wOBA, much less his xwOBA. The point here is not that Carroll was actually bad in his first month in the big leagues. It is just that his batted ball data was not indicative of a .250/.330/.500 hitter. Anyone penciling in an .800 or .850 OPS for next year as if it’s a mere continuation of what he already showed in 2022 should tap the breaks.
Before moving on to the pitching, the D-backs did have several hitters whose wOBA was actually lower their xwOBA, suggesting some positive regression could be in store moving forward. The clearest example of this is Christian Walker, whose .346 wOBA lagged 13 points behind his .359 xwOBA. Walker was arguably baseball’s unluckiest hitter in the first half of the season, so it comes as no shock that his final numbers still fell short of his expected stats. Still, he could be in for better fortunes in 2023.
The other notable under-performers from 2022 were Geraldo Perdomo and Carson Kelly, both of whom saw their wOBA lag 13 points behind their xwOBA. Even based on expected stats, though, neither had a great season offensively. Perdomo’s xwOBA was .269 and Kelly was .288. Even with some help from the batted ball gods, Kelly and Perdomo were still well below league average.
Heading into 2023, it’s worth noting that MLB’s new shift restrictions could help D-backs hitters significantly. Considering that all of the team’s biggest over-performers on offense bat left-handed, it’s not unreasonable to think that the new shift rules could help that group as much as regression to the mean might hurt them next year.
Before diving in, let’s introduce two new stats: xERA and xFIP. Both are ERA-estimators (read them like an ERA), but they operate differently. In essence, xERA is based on batted ball data while xFIP is based on strikeout rate, walk rate and reducing noise from excessively high or low home run rates that are likely to correct naturally in the future.
As a team, the D-backs outperformed slightly both in xERA and xFIP, but once again, the primary story here is which players in particular outperformed their expected stats. The list includes several of the D-backs’ most important pitchers moving forward.
Zac Gallen, of course, stands out most. His 2.54 ERA was significantly lower than both his 3.17 xERA and his 3.31 xFIP. Based on how xERA and xFIP are calculated, we can explain why these disparities exist.
First, the primary reason Gallen’s xERA was a half-run higher than his ERA is that he fared extremely well on batted balls. In fact, Gallen’s .237 BABIP (batting average on balls in play) in 2022 was the the second lowest in baseball among qualified starters, and the lowest ever by a qualified Diamondbacks starting pitcher. The league-average BABIP in 2022 was .289.
Despite the fact that pitchers do have some control over BABIP, hitters generally have more control over BABIP more than pitchers do. In Gallen’s case, having one of baseball’s best defenses behind him certainly helped keep his BABIP low, and that benefit that should continue into next year. Nonetheless, it will be nearly impossible to replicate a .237 BABIP again.
Switching to xFIP, the reason that Gallen’s mark of 3.31 — again, very good — was so far north of his 2.54 ERA was primarily because his strikeout and walk rates were good, but not elite in 2022. Gallen’s 26.9-percent strikeout rate in 2022 was actually the second lowest of his career. He had strikeout rates north of 28 percent in each of his first two big league seasons. Getting that strikeout rate back into the 28-29 percent range would go a long way toward making a mid-twos ERA sustainable in the future.
Like Gallen, Merrill Kelly also benefitted from a relatively low .269 BABIP in 2022, but the primary reason for his 3.86 xFIP was that he gave up only 21 homers in 200.1 innings. Kelly’s 0.94 home-runs-per-nine-innings (HR/9) is not necessarily unsustainable, but it’s hard to bet on, considering his career HR/9 is 1.19. What is certainly unsustainable is the 0.67 HR/9 Kelly had through Sep. 1. He gave up 11 of his 21 home runs in the final month of the season.
As for Madison Bumgarner, his ERA and xFIP were in nearly perfect harmony in 2022, but his xERA came in much higher at 5.53. That suggests that Bumgarner’s batted ball data — in particular, a 90.3 average exit velocity that was better than only eight percent of major league pitchers — was indicative of a pitcher with a much higher ERA than the 4.88 mark he had at the end of the year.
Drey Jameson’s story is similar to that of Corbin Carroll: The sample size is way too small to draw any definitive conclusions, but advanced stats suggest he might not have been quite as excellent as the surface numbers show in his four big league starts. (And, frankly, no pitcher can actually maintain a 1.48 ERA.)
In 24.1 innings, Jameson’s strikeout and walk rates were promising, but it’s worth noting that he gave up a lot of hard contact. Opposing hitters really got ahold of his four-seam fastball, in particular, with an average exit velocity of 93.9 MPH. Despite that, they somehow batted only .235 against it. Again, the sample is so small that there are no firm conclusions to be drawn about Jameson’s actual talent level — just that he won’t be able to dominate for long with that much hard contact on his heater.
As with the hitting side of things, it is worth mentioning that several D-backs pitchers actually underperformed their expected stats. On that front, Kevin Ginkel stands out most. Ginkel’s 2.90 xERA suggests his 3.38 ERA in 2022 might have undersold how good he actually was. (Again, insert obligatory small sample size warning here.) Moving forward, it’s not all that hard to see Ginkel developing into a backend weapon for the D-backs. His slider generated whiffs at an elite rate, and his four-seam fastball averaged 96 MPH and did not get hit particularly hard.
Outside of Ginkel, the only D-backs pitchers who meaningfully underperformed their expected stats in 2022 are no longer with the organization, including Caleb Smith, Sean Poppen, Reyes Moronta and Noé Ramirez.
That fact underscores a key takeaway: Many D-backs players outperformed their expected stats in 2022, and a handful underperformed, but almost all of the players who over-performed are being counted on in a big way next year, while most of the players who underperformed are either low on the depth chart or no longer in the organization.
Heading into 2023, we are left with a somewhat troubling picture for the D-backs. It’s not that they are doomed to fail, but they do have a lot to prove. On the positive side, many of the players who could be due for some sort of regression in 2023 are young and still on the upswing of their careers. No, they probably won’t have as many balls bounce their way in 2023, but also, maybe they’ll be just plain better and it won’t matter much.
Considering how talented the D-backs’ young core is, it’s not the type of group to bet against.
Top photo: Joe Camporeale/USA TODAY Sports
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