Why Zac Gallen's 2026 Results Aren't Telling an Honest Story

There are some concerns beneath the surface-level results.

Apr 1, 2026; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Zac Gallen in the first inning against the Detroit Tigers at Chase Field. Mandatory Credit: Mark J. Rebilas-Imagn Images | Mark J. Rebilas-Imagn Images

For the first time since the first week of April, 2025, Arizona Diamondbacks right-hander Zac Gallen's ERA is below 4.00. At 3.60 through four starts (20 innings), Gallen has started in two D-backs wins and two losses. He's 1-1.

Certainly, Gallen's results so far have been much better than last season's average pitching line. But they may not be sustainable. His underlying metrics, such as Fielding Independent Pitching and expected ERA, have been significantly less promising than his earned run total and overall success.

Throughout the right-hander's career, Gallen has generally seen either better or comparable peripherals as opposed to his ERA. At the very least, the numbers have been close — within less than a full run's difference.

His Cy Young-contending 2022 season ended with an 0.51 difference between his ERA (2.54) and FIP (3.05). His World Series 2023 season earned him a 3.38 FIP and 3.94 xERA beneath the raw 3.65 ERA.

And in fact, his abysmal 2025 was, still, underscored by better peripherals. Despite a career-worst 4.83 ERA, Gallen posted a 4.50 FIP and 4.28 xERA. While not overly impressive numbers, they did continue the trend between his raw results and underlying metrics.

But that hasn't been the case this season.

Why Zac Gallen's results may not be sustainable

Mar 26, 2026; Los Angeles, California, USA; Arizona Diamondbacks starting pitcher Zac Gallen (23) throws a pitch against the Los Angeles Dodgers during the fifth inning at Dodger Stadium. Mandatory Credit: Kirby Lee-Imagn Images | Kirby Lee-Imagn Images

After the worst season of his professional career in 2025, Gallen returned to Arizona on a one-year prove-it deal this offseason with a bit of a chip on his shoulder — an "edginess," as manager Torey Lovullo has described it.

And so far, hitters are hitting Gallen's stuff much harder than his run-prevention stats show. Gallen's xERA for 2026 thus far is a whopping 6.22. Essentially, the quality of contact against him has been deserving of much worse overall run-prevention.

The average exit velocity against the right-hander is 93.1 MPH — a ninth-percentile figure per Baseball Savant. His strikeout (12.9%) and whiff (16.7%) rates have each plummeted to seventh-percentile figures.

That has matched the eye test. Gallen has struck out just 11 batters in 20 innings against seven walks so far this season.

Transitioning away from being a swing-and-miss dependent pitcher is not necessarily a bad thing. In fact, it's a valuable skill to be able to pitch to contact consistently. But batted balls are traveling harder than ever off the right-hander this season. His hard-hit rate is over 50% for the first time in his career.

Apr 1, 2026; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Zac Gallen against the Detroit Tigers at Chase Field. Mandatory Credit: Mark J. Rebilas-Imagn Images | Mark J. Rebilas-Imagn Images

There is, of course, plenty of time for a peripheral resurgence. Four starts is not quite the sample size needed to give a full evaluation. The concern, of course, is that poor peripherals tend to lend themselves to negative regression of run-prevention results, rather than the opposite.

It's not all negative from Gallen, however. His four-seam fastball, which has been in decline ever since his 2022 breakout season, has been worth +2 Run Value while displaying a slight uptick in velocity — averaging around 94 MPH this season.

It's not that the fastball is a better pitch this season, with a career-low 93 Stuff+ rating (a metric that measures a pitch's movement and ride, in which 100 is average). Gallen is commanding that offering better so far, however. His Location+ metric on the fastball is up to 112 from the 99 it sat at in 2025.

But at a certain point, a 1.45 WHIP with an inordinate amount of hard contact will start to turn against a pitcher's ERA. The Diamondbacks do not need ace-caliber numbers out of Gallen, but some amount of improvement from 2025 is a necessity.

At a certain level, peripherals do not need to matter if a pitcher's run prevention stays consistently above the underlying metrics. All that truly matters is how many runs Gallen ultimately allows.

But these types of metrics do tell a story of what we can expect out of an arm — and Gallen's are not particularly promising despite the positive early results.

Only time will tell.