Three Diamondbacks Pitchers Who Could Outperform Projections

The Arizona Diamondbacks are set up to have a bounce-back from the pitching staff in 2025. Recently, Diamondbacks On SI concluded our series breaking down the individual player projections for the 2025 D-backs.

These projections are a composite of ZiPS and Steamer projections, prorated to our own playing time estimates.

While some players are projected more favorably than others, these numbers often more heavily weight recent seasons, while also frequently expecting heavy regression to the mean.

With that in mind, it's important to contextualize just how much one can rely on projections to deliver an accurate prediction of the coming year.

But for Arizona's pitching staff, these three arms seem set up to have a better 2025 season than what's being projected for them.

RHP Ryne Nelson

The Projection: 110.0 IP, 4.12 ERA, 6.3% BB, 19.4% K, 1.0 aWAR

Young righty Ryne Nelson shined in the latter half of the 2024 season. After a rough start to his D-backs' career, Nelson took an exceptional jump, becoming one of Arizona's most dominant arms.

He pitched to a pedestrian 4.24 ERA last season. That number is likely the culprit of projections that expect him to throw to a mere 4.12 number this coming year.

While the projection is improvement, it's clearly taking Nelson's ERA from 2024 a bit more heavily into account than it should.

Nelson began 2024 on a down note, looking closer to his 2023 self than any kind of improvement. But once the calendar turned to July, he was a different pitcher.

From July through the end of the season, Nelson pitched to a 3.05 ERA and 3.14 FIP. Though he did struggle somewhat in September, that was partially due to a right shoulder injury that kept him out a pair of starts.

Nelson began to land his secondary pitches, find ways to rack up strikeouts, and generally suppress opposing offense at a consistent rate.

And it wasn't a fluke. He tossed eight Quality Starts in his final 14 appearances, and punched out 80 batters from July through September, while only walking 16.

His K/9 (7.53) climbed a full strikeout and a half from 2023. He walked 2.03 batters per nine, nearly a full walk down from the previous year.

And to cap it all off, Nelson's 4.24 ERA was backed by a 3.74 FIP and 3.98 xFIP. By all accounts, he was a much better arm than his ERA showed, and a major improvement could very well be in order.

In 2025, it's not at all unreasonable to expect his ERA to dip into the 3.00's if he stays the course and continues to develop into a star.

RHP Ryan Thompson

The Projection: 55.0 IP, 3.71 ERA, 7.0% BB, 19.0% K, 0.4 aWAR

Sidewinding reliever Ryan Thompson has been one of the most reliable arms in the D-backs' bullpen since joining the club midway through 2023. He was intstrumental in stabilizing Arizona's relief corp on the way to a National League pennant.

In 2023, he allowed just one regular season run with the D-backs. In 2024, he began on a similarly elite pace.

As late as August 2, Thompson's ERA sat below 2.00, through 45.2 innings. From there, things began to deteriorate.

Once fatigue began to set in, Thompson started to lose his control, and began to get hit harder. He suffered several blowup outings in the final two months of the season, and finished with a more pedestrian, yet still very sturdy 3.26 ERA.

The projection expects even more regression. While it's understandable to imagine Thompson could fall victim to the volatility of the reliever ERA economy, nothing suggests he has truly declined as a pitcher, as his 3.30 and 3.35 xFIP FIP nearly matched his ERA.

Thompson had never pitched more than 47 innings in a season prior to 2024. Last season, he pitched 67. That's a sharp increase in workload for a reliever, and it's truly no mystery as to why he stumbled down the stretch.

So while regression is certainly possible, if manager Torey Lovullo does reduce his workload by any significant margin, it's quite likely Thompson could pitch better than his overall numbers in 2024.

And considering his projection expects a significant regression, Thompson wouldn't even need to beat his 2024 numbers. In fact, he could pitch worse than he did the previous season and still surpass his projections for 2025 quite handily.

RHP Zac Gallen

The projection: 146.0 IP, 3.70 ERA, 7.4% BB, 23.4% K, 2.4 aWAR

It was a strange season for righty ace Zac Gallen in 2024. While he displayed stretches of excellence, he also struggled with injuries and a bit of inconsistency on the mound.

As a whole, he was still a very effective pitcher, but didn't look like the dominant ace D-backs fans were used to seeing.

He did finish with a solid 3.65 ERA, and his 3.38 FIP suggested he had pitched somewhat better than that raw number.

But with the addition of ace Corbin Burnes, Gallen won't have to be the only one at the top of the rotation. In fact, an elite 1-2 punch could help Gallen return to his ace ways.

Regardless, Gallen's fastball was a bit of a sticking point in 2024. The four-seam, which had posted a +19 run value in 2023, dropped to -4 in 2024.

His command of the fastball was inconsistent, and that prevented him from setting up his secondaries, while also making him more prone to hard contact.

But looking at Gallen's projections for 2025, it seems more likely that Gallen will find a way to settle back in, rather than posting even worse overall numbers than 2024.

His strikeout rate has never been lower than 25% in a season, and he's only posted an ERA worse than 3.65 once in his career - the dismal 2021 season.

By all measures, it doesn't seem likely to see Gallen continue his downward trajectory. If he remains healthy and finds a way to even slightly return his fastball to its elite form, he, alongside Burnes at the top of Arizona's rotation, could be deadly again in 2025.

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