The Diamondbacks Needed Merrill Kelly Back in Their Rotation

It should be fairly obvious how well Kelly fits with Arizona, even with his age factored in. He is entering his age-37 season, but there are very few bells going off to worry about for his future performance.

The D-backs know exactly what they are getting out of Kelly. He’s a proven starting pitcher that will take the ball every fifth day and give them a strong chance to win those games.

If you ignore the COVID-shortened 2020 season and his lone injury-ruined season in 2024, Kelly has made at least 27 starts in every season of his career since 2019. He’s made 30 or more starts in four of them.

He’s pitched at least 177 innings in three of the past four years. That’s how Kelly earned the nickname Merrill the Mainstay from D-backs fans and announcers. In his 172 MLB starts, Kelly has an ERA of 3.77, an ERA+ of 113, a FIP of 3.99, 911 strikeouts, and only 300 walks in 1,008.1 innings.

He’s the definition of a new-age mid-rotation innings eater. The Phoenix native and ASU graduate had 28 starts of at least five innings in 2025. He went six innings or more in 19 of them. Plus, he is known for having a tremendous shot to pitch a quality start every time out. He made a quality start in 18 outings this past year.

Dating back to 2022, Kelly has been consistent, with 69 quality starts out of a potential 108, including three years with exactly 18 of them.

Kelly does all of this by spinning the ball better than nearly all other pitchers. He doesn’t wow anyone with velocity, averaging just 92 mph last season. However, he throws the kitchen sink at batters in all counts, leaving them guessing as to what he will throw. He can land all of his pitches in the strike zone at any time.

He throws a fastball, sinker, changeup, slider, curveball, and cutter. His changeup is his dominant pitch, and it’s befuddled hitters for years. Opponents hit just .203 against it last year and struck out on it a whopping 63 times.

The true worrisome pitch is his sinker, as hitters teed off on it for an average of .325. None of his other pitches had a higher batting average than .212, except the sparsely used curveball, which had a .277 average against.

His changeup and slider had whiff rates of 33.4% and 30.8%, respectively. Even though his Statcast page is full of blue, the top parts are sparkling red. Those parts are his pitching run values.

In 2025, he ranked in the 82nd percentile in overall pitching run value with 11, the 80th percentile in breaking ball run value with 5, and the 93rd percentile in offspeed with 6. Overall, it was a strong bounce-back season following a teres major strain in 2024.

Expectations for Kelly In 2026

As explained above, there’s very little reason to assume that Kelly won’t be a lock for at least 175 innings and 30 starts in 2026. He’s going to be one of the main pieces of Arizona’s rotation, guiding plenty of younger pitchers.

There should be no reason, except injury (which is always hard to plan for), that Kelly can’t keep soaking up innings and helping front a rotation that is trying to recover from a disastrous 2025 season and get back to October.

The Steamer projections from FanGraphs feel a bit low for what Kelly can do, but they are still serviceable. They project him for a 4.15 ERA, 31 starts, and 185 innings. Yet, Kelly has not had an ERA that high since 2021.

Kelly has already proven to be a pitcher and not a thrower, and he doesn’t overly rely on one pitch. He knows how to get whiffs and weak contact to get guys out. He’s a strike thrower, with a walk rate only once over 7.6% since 2019.

While he doesn’t strike many guys out, with a career strikeout rate of only 22%, he can get it done when he needs one, something that shouldn’t change as he gets older, thanks to his pitching style.

All of this is to say that Kelly knows how to pitch. He can get guys out reliably and win plenty of games for Arizona.

He has the chance to make some Arizona history this year too. He needs just 2.9 WAR to pass Zac Gallen for fourth all-time in team history, according to both FanGraphs and Baseball Reference. He also needs just four wins to pass Gallen for third all-time and 26 to pass Brandon Webb for second. Additionally, he’s 201 strikeouts from passing Webb and becoming second in team history.

The Arizona Diamondbacks needed Kelly back in their rotation. They had a glaring innings hole in there, especially after signing Michael Soroka, who isn’t exactly a proven innings eater. Now, they have plenty of innings taken care of. Kelly loves it in Arizona, and the fans love him. This was just one of those signings that made all the sense in the world and basically was a match made in heaven.

This was Arizona’s third move this offseason after bringing back James McCann to serve as backup catcher. There are plenty more moves to come in what should be a busy offseason for Hazen and company. The most pressing need is a closer, while the biggest question is whether or not they will trade Marte for a massive haul to potentially reset their competitive window.