Zac Gallen's Ugly Start vs Mariners Raises Further Questions

Another poor game for the Diamondbacks right-hander.

May 23, 2026; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Zac Gallen (23) prepares to throw a pitch against the Colorado Rockies during the first inning at Chase Field. Mandatory Credit: Anna Carrington-Imagn Images | Anna Carrington-Imagn Images

Arizona Diamondbacks right-hander Zac Gallen has been gritting his way through some tough, but not unproductive starts of late. He had given up five runs in his previous 11.1 innings over two starts — both of which were sturdy-enough performances to help his club secure wins.

But Friday night, against a talented, though admittedly somewhat struggling Seattle Mariners lineup, Gallen fell back into familiarly ugly territory. Ultimately, the Diamondbacks fell 7-6 in walk-off fashion.

The right-hander gave up five runs in five innings on eight base hits. He walked one — which came around to score — and gave up three home runs, including two from shortstop J.P. Crawford. The Mariners were all over Gallen through his short outing.

And so, the ever-persistent questions remain about Gallen's season, and future.

Zac Gallen's ugly outing furthers arsenal concerns

May 23, 2026; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Zac Gallen (23) throws a pitch against the Colorado Rockies in the third inning at Chase Field. Mandatory Credit: Anna Carrington-Imagn Images | Anna Carrington-Imagn Images

The largest question surrounding Gallen's performance this season has centered on the viability of his four-seam fastball. Once a weapon that paired well with a plus changeup and curveball, Gallen's fastball has been a rough offering in both 2025 and 2026 thus far.

Against Seattle Friday night, Gallen got three whiffs on his fastball despite inducing 17 swings. One of his three home runs came against that pitch, though his other two were on off speed and breaking pitches.

"Gallen is just somebody that's always tinkering, looking to get better," manager Torey Lovullo told Arizona Sports 98.7's Burns & Gambo Show prior to Gallen's outing on Friday.

"He's been grinding. ... yes, there are things that he's working on. The carry on his fastball, throwing it to the right place in the zone, throwing it to the right place out of the zone, just being versatile with the pitching and the selectivity and the sequencing, that's always crucial for him.

"I don't need him to throw 95 to 97 miles an hour. I want him to place that fastball exactly where he wants to, follow a game plan, and understand that when he hits a spot, there is a lot of swing-and-miss," Lovullo said.

Unfortunately, Gallen was not quite effective enough to deliver a quality outing. For the 2026 season, his ERA has risen back to 5.16. After posting a career-worst 4.83 ERA in the 2025 season, the hope was for a resurgent 2026.

Though Gallen has had some positive results this season, he's struggled with similar issues. He's posted a career-low 6.63 K/9 coming in to Friday, and his expected stats offer little respite from the poorer results.

"I thought there were some mistakes, some middle-middle mistakes," Lovullo said to D-backs.TV's Todd Walsh postgame.

"There were some situations where I thought he could have put away somehitters and he just couldn't, and he let the count linger. That's part of the game, that's part of it. Sometimes you execute, sometimes you don't. He just got beat today."

Diamondbacks fall to Mariners in extra innings

May 29, 2026; Seattle, Washington, USA; Arizona Diamondbacks third baseman Jose Fernandez (11) hits a RBI single against the Seattle Mariners during the sixth inning at T-Mobile Park. Mandatory Credit: Steven Bisig-Imagn Images | Steven Bisig-Imagn Images

The Diamondbacks put together a solid offensive effort against one of the best pitching staffs in baseball, plating six runs on 13 hits and four walks.

A struggling Geraldo Perdomo burst out with a 3-for-5 game, including a home run. Gabriel Moreno and Jose Fernandez both went 3-for-5 and Corbin Carroll went 2-for-6.

Arizona fought back from 3-0 and 5-1 deficits to knot the game at 6-6 off fireballing closer Andres Munoz, but could not scratch the go-ahead run across. They did not move the runner in extras, and Seattle would walk the game off on a Randy Arozarena double in the 10th inning.

Outside of Gallen, Arizona's bullpen was mostly solid. Brandon Pfaadt gave up a home run in 1.2 innings, but Taylor Clarke, Jonathan Loaisiga and Brandyn Garcia combined for a scoreless 2.1 innings. Juan Morillo gave up the walk-off hit in the 10th.