Can the Diamondbacks Survive Their Rotation Troubles?

The Diamondbacks did things the “right way,” to the extent that the right way means anything. After making the World Series unexpectedly in 2023, they went into the offseason with an exciting group of hitters and an unsettled rotation, so they opened the vault and signed two of the top-10 free agents that year — Eduardo Rodriguez and Jordan Montgomery — both starting pitchers. When those two flamed out in 2024 but the hitters kept producing, they went back to the well and signed Corbin Burnes, another marquee option. They refused to include top starting prospects in trades. They already had Zac Gallen and Merrill Kelly in the fold. This is how you build a top rotation.

Er, well, this is a way that you can build a top rotation, but this particular iteration hasn’t panned out. In Phoenix, things are falling apart on the mound. Let’s look through Arizona’s problem rotation spots (read: everyone other than Kelly) and see if we can find a solution for each before it’s too late for the team’s 2025 season.

Corbin Burnes

The Problem: Injury
Burnes got off to a slow start in the desert, but like the weather in his new place of work, he was heating up as the year wore on. His cutter isn’t quite the devastating weapon it was during his 2021 Cy Young season, but it’s still a menace. He’s still one of the best in the business when it comes to spinning breaking balls. A well-located Burnes curveball is an absolute masterpiece, a pitch that will make you question the very basics of physics and reality.

In Burnes’ most recent four starts, he’s gone nuclear: 31% strikeout rate, 2.19 ERA, 2.67 FIP. He’d also been stacking up volume: Three of his past five starts lasted seven innings. But the most recent start ended prematurely in the fifth inning, when Burnes felt sharp tightness in his elbow, saw his velocity drop, and left the game. Burnes said after the game that he didn’t know the severity of the injury, telling reporters, “I’ve never had anything like it before, so I really have nothing to compare it to.”

Injuries that Burnes has never dealt with before covers a broad range of possibilities, and as of Monday night, we do not know the status of his elbow. It could be anything from a medium setback to catastrophic, and it’s hard not to fear the worst. At the very least, most elbow injuries of this nature come with IL stints – even if the scans come back as pristine as possible, are the Diamondbacks sending him back out there next week? The recovery timelines are uncertain and often long. For the immediate future, the Diamondbacks have no choice but to operate as though Burnes won’t be back. The Diamondbacks need five starters on the active roster, and Burnes is unlikely to be one of them at this time next week. Someone has to fill his spot.

The Fix: Cry, then find backup plans
There’s no sugarcoating this one: It’s a bummer. Burnes has been one of the best pitchers in the majors for half a decade. He’s fourth in innings pitched over the past five years, third in WAR, second in ERA, sixth in FIP. He’s a bona fide ace heading into the back half of his career. And unfortunately, this is just how it goes when you’re a pitcher: Sometimes acts of your career are punctuated by arm injuries.

Luckily for the Diamondbacks, they have at least one internal solution who could be ready right away. Ryne Nelson has been good in a swingman role this year after a perfectly cromulent 2024 in the starting rotation. I’m a big fan of his keep-it-simple approach: He has a great fastball and a good cutter, definitely the two best pitches in his arsenal, and so he throws them a lot.

It’s a high-variance approach. When opponents are on the fastball on a given day, he doesn’t have many countermoves. But they usually aren’t on it, and Nelson has one tool that all starters covet: immunity to platoons. His entire arsenal lives on the north-south spectrum: vertical fastball, tight cutter, gyro slider, 12-6 curveball. He’s displayed a neutral platoon split for his career, and I completely buy it. When Nelson is cooking, he’s an uncomfortable at-bat for everyone, not just righties.

The reason he’s been bouncing in and out of the rotation instead of helping to anchor it is that he’s more of a soft-contact merchant than a bat-misser. You can chalk it up to the arsenal, if you’d like; he doesn’t throw any devastating sideways-breaking pitches to righties, and his changeup is better as an implication (I have this! I might throw this!) than as an actual out pitch against lefties. It’s really hard to deliver consistent top-tier starting results without strikeouts these days because hitters are quite good if they get their bat on the ball. That’s not to say that no one who mixes Nelson’s particular pitches can rack up strikeouts, but he hasn’t ever shown the ability, so I’m not betting on that changing overnight.

The Diamondbacks came into the year with more rotation options that they had spots, but instead of trading one of them away or not signing Burnes, they decided it was better to have too many guys than too few. The logic here is simple: You can never have enough depth of competent starting pitchers. The risk of injury is simply too high. Nelson is the obvious choice to slide into Burnes’ spot in the rotation, but if Burnes’ injury ends up not being too serious, the Diamondbacks should use Nelson to patch up some of this starting staff’s other holes.

There are plenty of questions surrounding the rest of Arizona’s depth. Yilber Díaz, the Diamondbacks’ top pitching prospect coming into the year, is back at the complex after struggling to throw strikes – he walked an eye-watering 31 batters in 30 innings of work in Triple-A. Cristian Mena, another top prospect, is already in the majors as a reliever, and I think the Diamondbacks are likely to leave him in that role in 2025, but I’m definitely willing to re-evaluate based on results, because his minor league numbers and top-shelf command are intriguing.

Bryce Jarvis has not looked the part in the big leagues, and the Diamondbacks seem intent on using him either as a reliever or not at all. Drey Jameson is now relieving instead of starting in the minors, and he’s still adjusting to the new role and his newly reconstructed elbow. If we’re talking dart throws, maybe Dylan Ray and Spencer Giesting will click, but I’m sure the Dbacks would prefer not to find out, at least at the big league level this year.

Zac Gallen

The Problem: Missing bats
Gallen is a persistently difficult pitcher to examine. I’ve never quite been able to wrap my head around his excellence. He throws a ton of pitches – fastball, curveball, changeup, slider, cutter – but really, it’s 50% fastballs with a wide variety of secondaries mixed in. His sharp, vertical curveball is the best of them, and he generally uses it as an out pitch, bouncing it or nibbling below the zone with two strikes.

In his best years, that curveball complemented a four-seamer that hugged the top of the zone and bamboozled opposing hitters. It was a fastball that excelled on the margins, though: 94 mph without outlier shape. He got a little bit more induced rise than average, and he threw it from a high arm angle, but in my head, it was a great pitch because of an accumulation of small advantages. Good but not great location, good but not great deception, good but not great shape – you get the idea.

On most of those axes, Gallen’s fastball has declined marginally in recent years. Its velocity is down about a tick from its peak; it was never imposing, but every drop in velo counts when you’re trying to miss bats without elite heat. Shape-wise, it’s now less vertical than you’d hope; he’s getting more tailing action than he did when the pitch was at its best. Not a huge change, but certainly one that makes things easier on hitters.

Our pitch models have picked up on all of these little changes. They think that Gallen’s fastball has gone from above average to slightly below average. The results agree. He’s barely missing any bats with it, he’s drawing very few chases on high fastballs, and after five straight seasons of getting excellent results with the pitch, it’s been below average for the past two years.

A lot of pitchers adjust to declining fastball utility by de-emphasizing the pitch. Secondaries are still underused across the league, in my opinion at least, and cutting out 10% of a so-so fastball to add curveballs and sliders often helps the fastball perform better; if hitters aren’t looking for it, they’ll do worse against it. But Gallen has resisted that change. In each of the past four seasons, he’s thrown his four-seamer between 46.3% and 49.1% of the time.

As best as I can tell, that fastball is dragging everything else down. He’s getting fewer chases and fewer whiffs, which means he gets ahead in the count less often. As a result, he’s had to use his curveball differently, spotting it in the strike zone when behind in the count more than ever before. That’s led to more loud contact. He does seem to like his slider as a get-back-in-the-count pitch, and I think it has good utility there, but he’s still learning it, and the location leaves something to be desired for now.

Gallen’s changeup is still great, despite a misleading decline in swinging strike rate. That’s not happening because the pitch has gotten worse; it’s happening because he has to use it at inopportune times more frequently. Only 27% of his changeups this year have come in two-strike counts. That rate had never fallen below 30% before, and was frequently around 35% when he was at his best. In other words, it’s the kind of pitch that bedevils hitters when they’re protecting. He also loves to throw it out of the zone and let hitters chase, but that’s tougher when his fastball isn’t getting him to two strikes all that often. That’s no knock on the changeup, though: In fact, it’s been his best pitch this year, piling up weak contact as batters fail to square it up.

The Fix: Fewer fastballs
It’s not rocket science, I know. But Gallen’s style of pitching – fastball dominant with nasty out pitches he likes to bounce – doesn’t work all that well with this particular fastball. His walk rate is up, his strikeout rate is down, and he’s never allowed more consistent dangerous contact. Something needs to change, but it doesn’t have to be something drastic if Gallen plays his cards right.

Gallen has always had good command of his secondaries, he’s just optimized that command toward two-strike pitches. Start throwing them early in the count more often, focus on in-zone sliders and changeups, and things could turn around quickly. If you liked Gallen when he was at his best, you liked him for his excellent, hard-to-measure skills: great command, great pitchability, a good understanding of how to mix and match his weapons to turn them into more than the sum of their parts. He can still do that – but not if he keeps operating off the plan from 2022 and 2023, which was created when his fastball had more utility.

Brandon Pfaadt

The Problem: Contact quality
Brandon Pfaadt got absolutely demolished by the Nationals on Saturday. That probably doesn’t describe it well enough: eight batters faced, six hits, two hit batters, no outs. That knocked his ERA above 5.00, and most of his advanced run prevention metrics are pointing the same direction. He has a 5.02 FIP and a 6.73 xERA. The metrics that regress home run rate – xFIP and SIERA – like him more, but Pfaadt has a long history of allowing more homers per fly ball than the average pitcher, so I’d take those two with a grain of salt.

Chalk the Nats game up to BABIP luck if you’d like, but those batters were on him. Four of the six hits were doubles. The worst expected batting average of the bunch was .310; four of the six were .650 or higher. In fact, this has been a constant throughout Pfaadt’s career: Opponents don’t always hit what they swing at, and he has great command, but particularly against lefties, where he shelves his excellent sinker/sweeper combo, he’s prone to allowing loud contact.

As fatal flaws for starting pitchers go, this is not the worst you could imagine. That would be “can’t throw strikes,” or perhaps “can’t miss bats.” But Pfaadt has yet to overcome this weakness so far in the majors. His career ERA is an ugly 5.06, and that’s over 340 innings, not a tiny sample. If the Diamondbacks are going to make the playoffs with him as a key part of the starting rotation, they’re going to need better results.

The Fix: Grin and bear it
When he’s at his best, Pfaadt scatters the hard contact he allows, limits walks (career 5.7% walk rate), and finds enough strikeouts and popups to tie the whole thing together. This profile can definitely work, and there have even been great pitchers who look like this. Max Scherzer springs to mind: Even as he’s become homer-prone during the last decade of his career, he’s still been one of the best pitchers in the game over that stretch. He’s done it by striking out a ton of guys, avoiding walks almost completely, and dominating with his slider so much that, for the most part, nobody was on base when the homers were hit.

Now, Pfaadt is not Scherzer (spoilers, I know), but you can at least see a path for Pfaadt to get league-average results here – or at least, I can. Tinker with the pitch mix a little, perhaps. Fewer curveballs to lefties would be a start. He’s thrown 100 of them and given up seven extra-base hits as compared to only 17 whiffs. That’s a poor ratio, to say the least. The average righty would pair about 39 whiffs with seven extra-base hits even against lefties. In other words, he just isn’t getting enough strikes with it to offset the noisy contact.

Relative to the rest of the problems in the rotation, I just don’t think this one is crying out for a fix. This is who Pfaadt is. He’s always going to have to find a Plan B against lefties; his best two pitches are most useful against righties. He’s always going to allow some loud contact; he’s a command-over-stuff type, and none of his pitches boast outrageous movement. Guys like this succeed all the time, though. Forget Scherzer, what about Pablo López? What about Luis Castillo, another sinker/slider guy who leaned into his changeup to solve his weakest matchups? Michael King succeeds like this. Even Merrill Kelly, Pfaadt’s teammate, does something similar.

In practice, the Diamondbacks are just going to let Pfaadt keep going. They don’t really have other options, considering those options are now needed to cover for Burnes. Pfaadt still has plenty of upside. In the context of the rest of their pitching struggles, letting him keep trying in the majors seems like the best option.

Eduardo Rodriguez and Jordan Montgomery

The Problem: A little bit of everything
Jordan Montgomery is out for the season; he never really established himself in the desert and had Tommy John surgery before this season started. His contract is up after this year, and there’s no love lost between him and owner Ken Kendrick. That leaves Eduardo Rodriguez from last year’s class of free agents, and he’s struggled with pretty much everything, too.

Injuries have kept him off the field. When he’s played, his kitchen-sink arsenal has looked flimsy, down in both velocity and movement. His 7.05 ERA this year is a caricature, but his problems – too many walks, not enough whiffs – are real. Worst of all, he’s not even providing them good volume when he’s healthy; he’s only completed six innings in two of his nine starts this year.

The Fix: Reframe expectations
The Eduardo Rodriguez who broke out with the Red Sox a few years ago is probably not coming back. That’s just life. By the time he signed with Arizona before last season, he might have been one of the top free agent starters on the market, but he wasn’t expected to be a Cy Young winner. Four years and $80 million doesn’t get that kind of arm these days. If you think of Rodriguez as a competent vet, a guy who should be your third starter when things are going badly and fourth starter when things are going well, his position on the team makes a lot more sense. He’s currently on the IL, but he’s expected back this week, and minor injuries are inevitable. If I were Arizona, I’d be happy to have Rodriguez back and be cognizant of his limitations.

I’m not even sure there’s a ton of tinkering to be done here. Rodriguez already operates on guile and deception. He mixes his pitches, liberally uses his great changeup, and is starting to throw his slider more frequently in place of his old fastball-heavy self. There’s a chance that he goes the Lance Lynn route and finds some extra strikeouts late in his career, but that wouldn’t be my central expectation.

A solid but unspectacular veteran isn’t what the Diamondbacks need most right now. Instead, what they need are some aces. But that’s not how real life works, and they’d certainly take some league-average innings. I don’t really think that’s a problem here. I agree with what our projection systems think: Rodriguez will be solid but hardly overwhelming the rest of the way. He won’t keep allowing a .376 BABIP, or a ridiculous 54% strand rate. Arizona’s problems are legion, but “the solid veteran we signed to be a solid veteran needs to start pitching like it again” is lower on the list of priorities than the other three vulnerabilities we’ve already discussed.

The Diamondbacks have faced a tidal wave of bad news on the pitching front this year. Burnes started the season slow, Gallen is still scuffling, E-Rod never quite got going, and Pfaadt just got put on a poster by the upstart Nats. Now Burnes is hurt and probably won’t be back soon. But despite that tough start to the season, there’s time to turn this around. The team is only three games below .500. The bats are hot. The talent on the pitching side is indisputable. The question now is whether Gallen, Kelly, and company can right the ship after a lackluster first third of the season.