Zac Gallen is getting the start on Monday night for the Arizona Diamondbacks as they open a three-game series at Chase Field in Downtown Phoenix against the San Francisco Giants. The Giants are going to send out Robbie Ray against Gallen and the D-backs.

Right now, Gallen has a 1-4 record with a pretty-high 5.65 ERA. Gallen has struck out 29 batters, walked 14, and has a 1.51 WHIP.

There have been times where Gallen has looked pretty solid. Then, other times, he's showed periods of struggle. Seeing his overall record and ERA is enough to give Diamondbacks fans some heartburn when he's on the mound.

Much like there are two sides to every coin, Gallen's season has a mix of both good and bad. 

Recently, an MLB.com story took a closer look at five Diamondbacks players who have that two-sided coin situation across their 2026 MLB seasons. Here's what MLB.com reporter Brent Maguire wrote up about Gallen.

First, let's size up his positives.

"Gallen has a 5.65 ERA in nine starts but he still has plenty of time to turn it around," Maguire wrote. "The velocity and pitch movement are largely in line with his career norms and he’s still only 30, so there aren’t many physical reasons to fret too much.

"Even with the decline he’s shown in recent years, he’s never been this bad, and some ERA indicators (4.69 FIP, 4.51 xFIP) suggest he should be a bit better."

OK, that's the good side. Now, what's lining up on the negative ledger for Gallen?

"That aforementioned decline is hard to ignore at this point," Maguire wrote. "His ERA and overall production has consistently regressed each season since his peak from 2022-23 and there are even more worrying trends this year.

"His strikeout rate is at a career-low 15 percent (he’s never been below 21.5 percent in a season) as is his 18.5 percent whiff rate," Maguire continued. "Until the whiffs come back, Gallen will likely continue to struggle."

In looking at Baseball Savant's 2026 MLB Percentile Rankings for him, Gallen ranks poor in Pitching Run Value and Breaking Run Value. In the pitching-specific areas, Gallen is putting up poor numbers in xERA, xBA, Fastball Velo, Average Exit Velo, Whiff %, K %, Barrel %, and Hard Hit %.

In eight MLB seasons, Gallen has a career 57-56 overall record with a 3.64 career ERA. So, his career numbers trend downward in the ERA category.

Gallen uses a four-seam fastball, slider, knuckle curve, changeup, and sinker in his pitching arsenal. He really leans on his four-seam fastball a lot, while his slider is his No. 2 option against opponents. Speaking of that slider, Gallen has elevated use of that pitch over the past two or three seasons.

That shows he has a lot of trust in what that pitch does against opposing hitters.

When he takes the mound against the Giants on Monday night, it will be interesting to see how Gallen mixes up his pitches. 

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