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Breaking Down the Diamondbacks Rotation

Hoping it doesn’t break down

Syndication: Arizona Republic Rob Schumacher/The Republic via Imagn Content Services, LLC

I’ve been expressing concerns about the Diamondbacks rotation for a while now. The team doesn’t project strong in any one area of pitching or offense, and there’s always been a sense since the beginning of the offseason of “where do you start?”

It all starts with starting pitching, at least in home games. I fear they’re going to be looking at crooked number deficits early in games and starters will be getting knocked out of the box early on a very frequent basis, putting the offense in a big hole to climb out of. That could make for a lot of discouraging games and short game threads.

A quick word about the offense. I think most would agree the offense has potential to rebound from last year’s 60 game doldrums and get back to something similar to 2019. It should be noted that 2019 hitting was right around league average. The team wRC+ was 93 and OPS+ was 94. NL Average is usually right around 93 or 94. (Pitcher hitting brings the NL Avg. below 100). While projected to be below average in 2021, it’s not hard to imagine getting back closer to that low bar this season. But even if they get back to average, is that going to be enough to dig out of the holes the starting rotation threatens to dig for them ?

The most up to date Depth Chart Projections at Fangraphs see the D-backs with the 25th best starting pitching in MLB, 12th in the NL, ahead of only the Rockies , Cubs, and Pirates . Report Link HERE

The above table is starting pitcher innings only. Players like Widener, Clarke, Young, Mejia and Duplantier are all projected to throw relief innings in addition to what you see above. (The bullpen ranks 24th by the way)

For historical context, the 2020 rotation had the highest FIP (5.12) 3rd highest ERA (5.04) and lowest WAR total (4.9 prorated to 162 Games) in Franchise history. REPORT LINK

4.65 ERA would represent a significant improvement over 2020 with many of the same pitchers logging the starts. But that would still rank in the bottom 13 in franchise history.

Going through the main 6 starters one by one I’m hard pressed to find optimism for beating these already pessimistic projections.

Madison Bumgarner, 5.04 ERA

He’s missed significant time with injury in 3 of his last 4 seasons. He’s seen diminished velocity losing a full 3 MPH off his fastball (91 in 2019 to 88 in 2020) and cutter (87 to 84 last year). He saw a very slight uptick in spring training this year, averaging about 89 on his FB. The reduction in velocity means he needs pin point command and increased dependency on his curveball.

In addition to relying more heavily on the curveball, he’s also experimented with Johnny Cueto like quick pitch trickery and the occasional drop down to sidearm. I don’t know how much of these kinds of developments the projections are able to incorporate. The projections are already bad enough due to things like batted ball profile, hard hit and barrel rates and the like. The reality is that he is now a low velocity junkballer that will need to re learn how to pitch at this level. Maybe he can do it, maybe not. The biggest thing in his favor is his legendary competitive fire. We’ll have to pin our hopes on that.

Zac Gallen, 3.87 ERA

His projections were already showing a significant increase in ERA due to the fact that through his first 150+ MLB innings his peripherals suggested an ERA a full run higher than his actual ERA. A good deal of regression to the mean is baked in. That said, I think everyone that watched him pitch and compete felt he was truly more than the sum of his parts. You can’t expect a guy to continue to beat his peripherals by a full run over the long haul. Since 1998 there are only a handful of starting pitchers with over 800 IP that managed to beat peripherals by even half a run. REPORT LINK . But his peripherals can certainly improve. He’ll need to lower his walk and homerun rates to keep his ERA under 3.00 in the future.

He was already slated for an innings limit, most likely around 150-160 tops. The projection here has him get 23 starts/129 IP isn’t that big of a dropoff. The real question is how will the stop and start in getting stretched out, and oh by the way, recovering from a fractured elbow, factor into his performance. The projection is not able to take that into account, so the projected ERA hasn’t changed. But we can. Spit balling it, how confident can we now be he’ll be better than that projection?

Merrill Kelly, 4.71 ERA

This is the guy I feel the highest level of confidence to be better than his projection by a half a run or more. I don’t expect him to contend for an ERA title, but I can see an ERA in the low 4’s for Merrill. Last year he had a 3.99 FIP and a 3.85 expected ERA at Baseball Savant. While that’s a good deal higher than his 2.58 ERA posted last year, and it was a short season for him, he pitched very well most of the time.

He looked pretty good to me in spring and does not seem to be suffering any after effects from the Thoracic Outlet Surgery he had last year. He’s stated he doesn’t feel it at all and doesn’t think about it unless asked, and his pitch velocity and movement seems to have not fallen off. 162 games is a long season, and there is always the risk he has a setback. We’ve all read and discussed the dangers with the type of surgery he had. But so far so good. I’m somewhat optimistic here.

Caleb Smith, 4.91 ERA

It’s already cliché to compare him to Robbie Ray. But to be fair to Ray, Smith’s first 4 seasons in MLB are not even in the same ZIP code when comparing head to head.

In Ray’s first 4 seasons, age 22-25 he posted 109 ERA+ and 6.6 WAR in 492 IP

Smith’s first 4 seasons, age 25-28 he posted 92 ERA+ and 2.1 WAR in 263 IP

I haven’t seen anything from Smith, either in his command of his stuff or in his pitch execution to lead me to believe he will be anything remotely resembling consistent.

Luke Weaver, 4.53 ERA

In 2019 his peripherals matched his ERA and he looked dominant at times. Unfortunately an elbow injury sidelined him 1/3 of the way into the season and he simply hasn’t been able to get back to anything like that stretch of success. His gopher ball problem is extreme, and he appears to now be a two-pitch pitcher. The FB and changeup are good, but neither of his breaking pitches, slider or curve are working for him. It may not be a coincidence that he was slotted in the 5th spot. While there may be several candidates for demotion due to poor performance as early as May, Weaver is clearly in the dog house and his rotation slot may be the most vulnerable. I’m on record as believing his FB/CH combo with the occasional curve/slider mixed in would play in a late inning short relief role.

Today Matt Herges spoke to the media. He mentioned that Weaver’s changeup was elite, but there was a lot of conversation about what he needs to do to be successful. Besides continue working on the slider, he had these comments:

  • Luke needs. “Full conviction intensity from pitch one”
  • “Pacing himself doesn’t suit him”
  • “It seems Luke is at his best when he comes out not hair on fire, but ready to compete with his best pitch from the very first pitch on”

I then asked Matt if the pitching personality he just described was more that of an elite late inning reliever. He gave a knowing chuckle at that question, and it felt like it’s something that has been discussed. But ultimately he said he’s not ready to send Luke to the Bullpen.

Listen to Herges’s full comments on Weaver below, or here:

Taylor Widener, 4.76 ERA

He’s shown flashes of recovering from his Reno debacle of 2019, and as Jim said to me on text if his slider can get back to what it once was perhaps he could surprise us while filling in for Gallen, and who knows, may end up replacing Weaver or Smith when Gallen returns. His start on Tuesday was a breath of fresh air. He gave up a couple of solo homers and had to work out of a bases loaded jam in the 4th, which he managed to do. But he went 6 23 innings on 86 pitches only giving up the two runs and striking out 7. His slider looks improved. So there is some honest to goodness hope here for a mini breakout. There’s always one unexpected guy that out performs expectations. Why not him ?

Corbin Martin, 4.69 ERA

Nobody has any idea what he can really do. I can’t evaluate this projection or this pitcher. I haven’t seen enough of him and there isn’t enough of a statistical track record. So for now he’s simply a replacement level pitching prospect with upside if he can remain healthy and find command. That description applies to a slew of pitching prospects.


I know this is an overly pessimistic article, even by my standards. The 4.65 projected ERA is already bad enough. But I honestly think the “collapse rate” whereby the rotation posts over a 5.00 ERA again is about 20%, and the “breakout rate” where they come in under 4.30 is only about 10%. The fan in me prays I’m dead wrong, and I’ll need to write a mea culpa article in a few months. That does happen every 5-6 years. Maybe this is the year!