Sep 20, 2025; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Zac Gallen (23) pitches against the Philadelphia Phillies during the third inning at Chase Field. Mandatory Credit: Joe Camporeale-Imagn Images Joe Camporeale-Imagn Images

Former D-backs Ace Had Controversial 2025

Originally posted on Arizona Diamondbacks on SI
By Alex D'Agostino | Last updated Jan 27, 2026 8:00 AM ET

The Arizona Diamondbacks' 2025 season was marred by injuries and underperformance, and right-hander Zac Gallen was one of the more notable examples.

Gallen struggled to an extreme degree for much of the season, but began to display notably improved numbers in the second half. Still, the former ace ended the year with his worst major league season's worth of results.

As Arizona Diamondbacks On SI continues to break down the individual seasons of every player that contributed to the 2025 D-backs roster, the below article will be updated with the proper links to every season review as they are published.

Arizona Diamondbacks 2025 Player Review: Zac Gallen

Alex D'Agostino

Gallen's 2025 was, essentially, a tale of two seasons. Following his breakout 2022, the right-hander had seen a drop-off in numbers in both 2023 and 2024. There was hope for a resurgent season, but 2025 began on as brutal a note as could have been expected.

Through his first six starts, he held an ERA of 5.57. He showed signs of coming out of that slump in May, but two Quality Starts to open the month were followed up by more rocky outings. He sprinkled some quality outings in between, but generally continued to struggle.

Until the Trade Deadline passed.

Gallen was one of the free agents on the market, but no team was willing to give up reasonable assets to acquire him. For an arm that had been hailed as an ace in years prior, that was, perhaps, a wake-up call.

And he began to pitch as if that were the case. Following the Deadline, from August 1 forward, Gallen posted a 3.32 ERA in 11 starts. Of those 11, eight were official Quality Starts.

He finished the season with his worst career strikeout rate (21.5%), though his walk rate improved marginally from 2024 (8.1% vs 8.7%). He remained healthy for the duration, making 33 starts and completing a workhorse 192-inning load.

His fastball improved somewhat, as well, but it was still a -2 Run Value pitch per Statcast, well down from his ace-like years — though it did not suffer for velocity. If Gallen wants to revitalize his career, it will have to be on the back of that pitch.

Zac Gallen: 2026 Outlook

Gallen declined the D-backs' Qualifying Offer, as expected, and entered free agency. It was generally thought he'd command a $100-plus million contract elsewhere, but that market has yet to materialize.

In fact, a potential reunion is becoming increasingly possible, as a recent report suggests Arizona is the leader in the race to sign him.

If he does sign elsewhere, the D-backs will gain a compensation draft pick. A total value of over $50 million would give Arizona a pick just following the first round, while anything less — which could very well be the case — would see the pick fall to between the second and third rounds.