Could Zac Gallen Have a Career Season in 2025?

Fully healthy, and with some added rotation help in a contract year, Zac Gallen could smash his projections in 2025.

Sep 25, 2024; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Zac Gallen (23) throws in the first inning against the San Francisco Giants at Chase Field. Mandatory Credit: Matt Kartozian-Imagn Images / Matt Kartozian-Imagn Images

This article is part of a series reviewing the projections for each member of the Arizona Diamondbacks 40-man roster, as well as select prospects and non-roster invitees. The order of presentation was chosen using a random number generator.

The projection is comprised of the average of ZiPS and Steamer rate statistic projections, which can be found on FanGraphs. The playing time projections are our own, based on our estimates. As the D-backs make further moves throughout the offseason, the playing time projections will be updated, and relevant counting stats such as home runs and WAR can be updated.

RHP Zac Gallen, 29

Zac Gallen statistics and 2025 projection / Alex D'Agostino / Diamondbacks ON SI

Why Gallen might outperform this projection

It's easy to look at some of the recent struggles of right-hander Zac Gallen and assume that his ceiling has already been reached.

In 2024, he struggled with injury, consistency and command, and despite putting forward a very respectable 3.65 ERA and 3.38 FIP, he didn't quite look like the dominant ace that Diamondbacks fans had come to know.

But with sights set ahead to 2025, there lurks a chance that Gallen's true prowess lies dormant, waiting to be unlocked in the coming season.

As recently as 2022, his 2.54 ERA mowed down opponents in his path. In 2023, he pitched a career-high 210 innings and helped lead the D-backs to the World Series. By all accounts, Gallen's stuff and smart pitching lands him in the upper tier of MLB starters.

With that said, he was limited in 2024. A nagging hamstring injury held him to just 148 innings. His numbers were solid, but not elite.

With recency bias in mind, it's easy to look at a projection that expects a good, but not great 3.70 ERA and a notably decreasing K%, and assume that he might be in for a less-than-stunning 2025 season.

But in truth, there's a high likelihood that Gallen is set up for a brilliant 2025, perhaps even one of his career-best years.

The addition of ace Corbin Burnes to the rotation, at least on paper, immediately bolsters the top of the rotation. With no disrespect to Gallen or his role as the ace of the staff over the past three seasons, Burnes presents his 2021 Cy Young award and 2.92 2024 ERA as the case to take over as the new no. 1 starter.

Not only should the pressure be taken off Gallen's shoulders in the short term, the addition of Burnes also brings another dynamic to the table.

Knowing Gallen to be the competitive, chip-on-his-shoulder pitcher he is, the addition of a bona fide ace, in all likelihood might provide motivation to kick his game into a higher gear and deliver a true ace season.

Gallen is also a free agent in 2026. Contract years often make for some of the best statistics, as he's sure to garner massive contract offers across the league after 2025's conclusion.

That, plus a new pitching coaching staff, could lead to a resurgent year from the righty. Don't be fooled by some of the inconsistencies - he has been an excellent pitcher in his time with the D-backs.

If Gallen's stuff continues to play, and he avoids injury, surpassing a 3.70 projected ERA will come easy for the 29-year-old.

A 23.4% strikeout rate also appears to be a heavy undersell when he's never onced seen that number dip below 25% in a season. In fact, 2024 was the first year his K rate dropped below 26% in a season - with the average sitting at 22% league-wide.

Everything will have to go right for Gallen to look like his 2022 self again, but the stars do seem to be aligning for a very good year from the right-hander in 2025.

Why Gallen might underperform this projection

While some of Gallen's poorer outings were unlucky, and he was still an excellent starting pitcher in 2024, there was one major concern for the ace: his fastball.

The fastball, which has profiled as Gallen's best multi-purpose weapon, saw a significant drop in 2024. In 2023, a year that even by itself wasn't Gallen's best, his four-seam fastball posted a +19 Run Value.

In 2024, that number plummeted to -4. The fastball isn't his only weapon, as Gallen holsters a diverse arsenal. However, putaway pitches such as his knuckle curve and changeup rely heavily on the consistency of his fastball in order to tunnel well enough to deceive hitters.

In 2024, Gallen struggled to throw the fastball for strikes consistently, or frequently left it in hittable spots. Both his average exit velocity and hard-hit rate took a huge step below league average last year.

That lack of deception led to a reduced, but still above average strikeout rate (25.1%), a more pedestrian 3.65 ERA, and a concerning increased walk rate.

His BB% increased from 5.6% in 2023 to 8.7% in 2024. His walks per nine jumped from 2.01 in 2023 to 3.28 in 2024.

If things continue in that direction, there's a decent chance Gallen can't reach his projected ERA or strikeout rate, and his walks will continue to rise, especially if his confidence begins to waver.

Summary

Despite some of these concerns, even a "down" year for the ace still presented a quality season. It's also quite possible he was dealing with fatigue in 2024, after pitching an enormous 243.2-inning workload across 2023 (postseason included).

There's a chance that his 2024 hamstring issue also hindered his mechanics in a way that reduced his effectiveness on the mound as well.

Nothing is certain in baseball, but it seems foolish to go into the 2025 with expectations that Gallen won't live up to what is a relatively modest projection, though he could still fall below it if his fastball continues to deteriorate.

Regardless, Arizona's rotation will look quite different in 2025. If Gallen struggles again, then perhaps a free agency departure is best for all parties.

But with the support of Burnes, a fully healthy season, and a looming opportunity in free agency, Diamondbacks fans could be in for one of Gallen's best seasons to date.

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Arizona Diamondbacks 2024 Player Review: Zac Gallen