Looking at the Diamondbacks 2021 rotation

When we polled fans about the areas of concern at the end of last season, there was no doubt that pitching was far more a concern than the position players. Combining the rotation and bullpen, that got 90% of votes, with the infield and outfield receiving only a tiny fraction of that combined. There was a fairly close split between starting pitching and relievers, with the latter winning out by a 49-41% margin. We’ll get to the bullpen next week, but let’s look for now at the rotation, which so far looks largely set to be the same people who started games for the Diamondbacks last year.

2020 rotation

Below, you’ll find everyone who started for the D-backs last year. The numbers are their ERA, starts and bWAR - the first and last figures also include any relief appearances they may have made.

• Zac Gallen - 2.75 12 2.7
• Luke Weaver - 6.58 12 -0.2
• Madison Bumgarner - 6.48 9 -0.3
• Robbie Ray - 7.84 7 -0.4
• Alex Young - 5.44 7 0.0
• Merrill Kelly - 2.59 5 1.4
• Taylor Clarke - 4.36 5 0.6
• Caleb Smith - 2.45 3 0.3

Overall, the D-backs rotation was not great. They ranked ninth in the National League by bWAA from their starters, and a woeful fourteenth by fWAR, ahead only of the Pirates. The team’s rotation FIP of 5.12 was the highest in franchise history by quite some way, shattering the previous worst of 4.70, set all the way back in Arizona’s inaugural season of 1998. They managed only ten wins over the sixty games played: even pro-rated to a full season, that’s still seven fewer than the next worst, the inept 2004 rotation. Gallen and Kelly were the only pitchers to deliver a quality start. It’s generally safe to say that things should be better this year - if only because they really can’t get much worse.

2021 candidates

With the exception of Ray, all of the above figure to be in the mix for sports in the rotation again this year. Almost regardless of who replaces Robbie’s seven starts, it shouldn’t be hard for them to deliver better than the 7.84 ERA he gave the D-backs in 2020. But it’s safe to say that just about all of the candidates have question-marks of some kind about their potential performance this season. Let’s go through them and see what kind of answers are available.

Zac Gallen: Can he repeat his 2020 performance?

Sadly, the answer is most likely “not,” despite getting a morsel of Cy Young love this year. Oh, make no mistake: he’s still going to be good. But it’s probably too optimistic to expect a sub-three ERA again this year, much though we’d still love to see it. In both 2019 and 2020, his FIP was around 3.60-3.70, and that’s generally a better predictor of future performance than straight ERA. As Wesley mentioned in the player review, Zac beating that in “real” ERA for 2021 will depend on him either continuing to generate softer than average contact, or an improvement in his peripherals, such as cutting back on the walks. He is still only aged 25 though, so getting better is by no means out of the question.

Luke Weaver: Will the real Luke Weaver please stand up?

Weaver made 12 starts for the Diamondbacks in both 2019, and 2020, but the results could hardly have been more different:

• 2019: 64.1 IP, 55 H, 22 R, 21 ER, 6 HR, 14 BB, 69 SO, 2.94 ERA, 3.07 FIP
• 2020: 52.0 IP, 63 H, 39 R, 38 ER, 10 HR, 18 BB, 55 SO, 6.58 ERA, 4.67 FIP

His ERA doubled, and his FIP spiked by more than 50%, Some of that was likely bad luck. His BABIP increased by 57 points, to a figure of .349 that was well above league average, even as his line-drive rate dropped to a career low of 19.3%. In particular, ground balls had a .321 BABIP for him, almost a hundred points above league average for those (.226). I would be expecting some positive regression, but after last year, I think I’d be more than happy with anything approaching a four ERA

Madison Bumgarner: Was that Mason Saunders’ last rodeo?

We didn’t expect to get the MadBum who was a four-time All-Star from 2013-16, with only Clayton Kershaw and Max Scherzer posting more wins over that period. But we didn’t expect career worsts for home-run and strikeout rates, leading to an ERA worse than any other in Bumgarner’s career, by more than two and a half runs. His average fastball was three mph slower than in 2019, at a pedestrian 88.4 mph; while it’s hard to say if that caused the struggles, I’m fairly sure it didn’t help. Madison did finish the year strong, with back to back outings of five scoreless innings, which gives a glimmer of hope. But the “cheap” first year is gone, and he’s due $19 million thus season. Hopefully, he’ll pitch like it.

Alex Young: Would he be better in the bullpen?

At first glance, there was a clear difference in Young’s numbers between starting and relieving in 2020, which would appear to suggest he might be better off working long relief. In Young’s 7 starts, he went 0-4 with a 6.03 ERA. Over his 8 bullpen outings, Alex was 2-0 with a 4.20 ERA. However, a lot of the difference can be chalked up as the result of drastically different BABIP: .337 as a starter, vs. .177 in relief. Elsewhere, the gap in performance was harder to see. For example, there was little or no difference in his K:BB ratio - 2.80 against 2.75. Obviously, his value would be greater in the rotation, due to the higher number of innings pitched. But his performance has to justify it.

Merrill Kelly: How’s his health?

When healthy last season, Kelly was great. Again, like Zac, maybe not quite the sub-three ERA he delivered, but he produced some sterling work. It was definitely unfortunate, when surgery for thoracic outlet syndrome cut his season short, ending it after five starts. Given the resulting uncertainty, there were questions as to whether the team would pick up his $4.25 million option for 2021. But the D-backs - presumably more informed about the situation than fans - exercised it. There are no guarantees with this procedure, so spring training promises to be particularly for important for the pitcher, and his outings will be closely watched for indications as to his recovery.

Taylor Clarke: Can he sustain his improvement?

Keegan called Clarke his “favorite replacement level player” on the D-backs this year, but also thought Taylor trailed only Merrill Kelly as Arizona’s most improved man. He shaved close to a run off his ERA, and his flexibility was valuable, with Clarke doing a good job of bouncing between the rotation and bullpen as needed. However, there’s still room for him to get better. He gave up too many long balls, and Taylor probably also needs to get the K:BB ratio north of two if he’s to become a credible long-term solution. As a back of the rotation guy earning league minimum, you could probably do worse. Yet I’m not sure whether his ceiling is high enough to make him a longer-term option.

Caleb Smith: Is he a flash in the pan?

Smith came over from the Marlins in the Starling Marte deal, and not too much was expected of him. Before this season, he had made 46 major-league starts for the Yankees and Marlins, with an overall ERA+ of 89. He even led the league in home-runs allowed in 2019. But over three starts and a relief appearance for the D-backs, he looked considerably better, allowing only three earned runs over 11 innings, and striking out better than a batter per frame. But there are still obvious issues: he walked six batters, most obviously, and that rate isn’t a sustainable path to success. But much like Gallen, if he can harness better control, it’s possible Smith alone could make the deal a win for Arizona.

New faces for 2021?

On the MLB.com list of the Diamondbacks’ top 30 prospects, there are three pitchers currently listed with an ETA of this year. By coincidence, two of them came over from the Astros in the Zack Greinke trade. Probably the one we’re most likely to see is right-hander Corbin Martin, though he will first have to prove his health, having had Tommy John surgery in July 2019. He had been seen as an overall Top 100 prospect before that, and Corbin had been on the D-backs radar for a while, first as a draft pick, then in talks about Goldy going to the Astros. He won’t be rushed back, but it will be interesting to see whether he’s seen as a contender for a spot in spring training.

The other two pitchers are J.B. Bukauskas and Josh Greene. The latter, fingers crossed, might be the reincarnation of someone we know. By that, I mean a relatively unheralded pick (14th round in this case) whose calling card, per MLB.com is “a low- to mid-90s bowling-ball sinker that helps him induce ground balls at an elite rate.” That remind you of anybody? Bukauskas may end up following the Archie Bradley route and going to the bullpen, behind his fastball/slider combination. But Arizona seems intent on giving him every chance as a starter first. His control and command will likely determine J.B’s eventual role for the D-backs.

I’d be curious to see in what order you rank the above candidates, in terms of their 2021 value to the team. Gallen would appear the obvious #1, but thereafter... Well, what do you reckon?