What Should the Diamondbacks' Rotation Look Like in 2025?

With the new addition of a Cy Young-winner in Corbin Burnes, the D-backs find themselves with an excess of starting pitching.

Sep 8, 2024; Houston, Texas, USA; Arizona Diamondbacks starting pitcher Ryne Nelson (19) reacts after a pitch during the first inning against the Houston Astros at Minute Maid Park. Mandatory Credit: Troy Taormina-Imagn Images / Troy Taormina-Imagn Images

The Arizona Diamondbacks are facing a situation they've been quite unfamiliar with in recent years: a surplus of serviceable starting pitchers.

With the shockingly monumental recent signing of ace and Cy Young winner Corbin Burnes, the D-backs now have a total of seven starting pitchers on the MLB roster.

A seven-man rotation is out of the question, and it's not incredibly likely that Arizona will go with a six-man rotation either. So, what exactly should they do with all their starters, and what should the rotation look like going into the 2025?

First, let's take a look at the available starting MLB arms:

RHP Corbin Burnes

Burnes' six-year, $210 million deal was recently made official. He's a bona fide ace, the 2021 NL Cy Young winner, and has pitched to sparkling numbers throughout his career.

He's coming off a 2024 that saw him pitch to a 2.92 ERA, and he's projected another good season in 2025. For his career, he's posted a 3.19 ERA and 3.21 FIP. While his strikeout rate is down from his normal number, he began to revive it in the latter end of 2024.

Whether or not he figures to be the immediate ace over Zac Gallen has yet to be seen, but Burnes will certainly sit near the top of Arizona's rotation.

RHP Zac Gallen

Zac Gallen has been Arizona's top starter since his breakout 2022 season. He finished third in Cy Young voting in 2023, but stumbled a bit the next season.

In 2024, Gallen pitched to a 3.65 ERA (but 3.38 FIP), but dealt with injury issues and inconsistency. As a whole, he's still one of the better arms in baseball with excellent stuff and command, and should be set up for success with Burnes alongside him in 2025.

RHP Merrill Kelly

Merrill Kelly was down for most of 2024 with a shoulder injury, and also dealt with a recurrent cramping issue on his return. He pitched to a 4.03 ERA in just 13 starts.

It's unknown whether the 35-year-old Kelly will return to full form, but he's been a model of consistency with the D-backs, and it's hard to place full judgment on a season so beset by injury struggles.

LHP Eduardo Rodriguez

Arizona's marquee signing in the 2023 off-season, the veteran left-hander spent most of 2024 on the Injured List with a shoulder strain.

On his return, he pitched to a poor 5.04 ERA and 4.57 FIP over only 10 starts. It's understandable to see poor results after a major shoulder injury, but at age 31, there's concern over whether he'll be able to perform and remain healthy in 2025.

RHP Brandon Pfaadt

Young righty Brandon Pfaadt pitched a career-high in innings in 2024, leading the D-backs in that category. He pitched 181.2 innings over 32 starts and showcased major growth in year two.

It wasn't until the waning weeks of the season that he began to break down, and his 3.61 FIP is a much better indication of his overall success than his 4.71 raw ERA.

RHP Ryne Nelson

Ryne Nelson made a spectacular leap in 2024. After a poor 2023 and rough start to 2024, he became one of the D-backs' biggest success stories, as he pitched to an eventual 4.24 ERA and 3.74 FIP.

He was absolutely dominant through July and August, and despite landing on the Injured List in September, the 26-year-old became one of Arizona's most valuable arms down the stretch.

LHP Jordan Montgomery

The big lefty's disastrous 2024 saw him pitch to a 6.23 ERA and 4.48 FIP while struggling with command, movement and velocity.

He was eventually relegated to bullpen duties, despite being on a contract worth $25 million. He picked up his $22.5 million player option for 2025, but the D-backs are likely looking to move off Montgomery and his large contract - a factor that appeared to hinder their Free Agency moves prior to the Burnes signing.

Roster Dilemma

So, with seven starters in the rotation, decisions will have to be made.

Diamondbacks ON SI's Jack Sommers has written extensively about Montgomery's trade value, noting that the D-backs have made an effort to shop him. It's simply a matter of how much of Montgomery's contract a potential trade partner would be willing to eat.

With that in mind, the D-backs are likely content to enter Spring Training with all seven arms, Montgomery included. If Montgomery can put together some positive showings in the spring, his trade value could rise.

Another factor to keep in mind is the threat of injury. With some recent concerns surrounding Gallen, Kelly and Rodriguez in the health department, there's a decent chance Arizona's rotation decisions end up being sorted out from necessity, and they don't make it to Opening Day with seven healthy starters.

On the flipside, injuries are sure to plague other clubs as well. Depending on how late injuries may occur, a team could end up being desperate for starting pitchers, and call on the D-backs, willing to take on Montgomery's salary.

Of course it's not just Montgomery. There's always a possibility Arizona moves Kelly, either of their younger arms, or even Zac Gallen, though that possibility is quite distant at this time.

As Jack Sommers wrote last month, Nelson and Pfaadt would bring the highest trade value based on their control. However, that amount of value would likely be used to bring in a controllable hitter, rather than a starter or reliever.

AZCentral's Nick Piecoro noted in an article that the club has reiterated the goal of fielding the best possible team in the coming season - suggesting Gallen and Kelly are likely safe from potential trades.

Analysis

A Montgomery trade feels somewhat inevitable, although it could take longer to materialize - well into Spring Training. As Piecoro wrote, the D-backs appear content to bring their surplus of arms into Spring, and while a six-man rotation might not seem likely, it's not completely off the table.

Ultimately, the D-backs will likely need to move someone. Barring injury, it seems probable that their rotation will go as follows: Burnes, Gallen, Kelly, Rodriguez, Pfaadt, with Nelson serving as a swing-man or long reliever, given his experience and success out of the bullpen.

It's also possible that Nelson forces his way back into the rotation full-time. If Pfaadt struggles, Nelson could replace him as the fifth starter.

While it doesn't seem likely that Rodriguez would be in danger of losing his slot due to his veteran status and contract value, the southpaw is also an arm with plenty of question marks surrounding him. If the D-backs truly want to have the best possible team on the field, no one is totally safe, and Nelson could easily earn more innings than currently projected and solidify himself as a dominant starting pitcher.

Injuries are, of course, unpredictable. It's quite possible the rotation might look different than any of us may anticipate. But with the addition of Burnes, and even a modicum of improved health, it seems that the D-backs' rotation will be set up for a better 2025.

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