If you just glance at the surface of the Zac Gallen game log from this past year, it looks like a total car crash. Honestly, a 4.83 ERA for a guy who was a Cy Young finalist just a couple of seasons ago? It's jarring. You'd think the "Milkman" had finally run out of steam or that the heavy workload from Arizona's 2023 World Series run had permanently sapped his arm. But baseball is rarely that simple.
The story of Gallen's 2025 season is actually a wild tale of two very different pitchers. One was a guy struggling with home runs and a fluctuating slider in the spring; the other was a dominant force who quietly became one of the best starters in the National League over the final two months.
The Numbers That Sting
Let's get the ugly stuff out of the way first. Gallen finished 2025 with a 13-15 record across 33 starts. For a pitcher of his caliber, those 15 losses are a career high and a tough pill to swallow. He also surrendered 30 home runs—the most he’s ever given up in a single campaign.
The trouble started early. In April, he was rocking a 5.08 ERA. By June, things got even worse, with his monthly ERA ballooning to 6.23. It wasn't that his velocity was gone, although he did dip to about 93 mph on the heater for a stretch. The real issue was a mix of poor location and a slider that just wouldn't bite.
Basically, he was living in the middle of the plate. When you throw a 93 mph four-seamer to big-league hitters without perfect command, they're going to park it in the bleachers. And they did. Often.
The Turning Point in the zac gallen game log
Most fans probably checked out on Gallen by July. That was a mistake. If you look at the zac gallen game log from August onwards, you see the "Ace" version of Zac Gallen return.
He didn't just get lucky; he changed his entire approach. He started leaning more on a sinker to keep right-handed hitters from pulling the ball for power. He also rediscovered the "feel" for his slider.
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Late Season Surge
Look at this late-season stretch that almost saved his stat line:
- September 3 vs. SF: 6.0 IP, 1 ER, Win.
- September 15 vs. SF: 6.0 IP, 1 ER, 6 K, Win.
- September 20 vs. PHI: 7.0 IP, 3 ER, 9 K, Win.
By the time September rolled around, he was pitching like a man possessed. He went 4-0 in his final five starts of the previous year (2024), and he brought that same "finisher" energy to the end of 2025. Over his last nine outings, he posted a 2.68 ERA. That is a massive swing from the 5.00+ ERA he carried through most of the summer.
Why the Slider Matters So Much
Gallen has always been a "tinkerer." He’s a perfectionist, sometimes to a fault. In 2025, he started the year using the slider nearly 24% of the time against righties. That was a huge jump from his career norms.
The problem? The pitch lost its vertical drop. It became "flat."
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When a slider doesn't slide, it's just a slow, spinning fastball. Hitters crushed it. He actually scrapped the pitch almost entirely in June, throwing it less than 4% of the time. But in August and September, he brought it back with a different shape. He stopped trying to make it a power pitch and focused on the movement. The results were instant. In September, right-handed hitters literally couldn't touch it—he held them to a .000 average on that specific pitch.
Looking Ahead: Free Agency and 2026
Despite the high season-long ERA, the Diamondbacks didn't hesitate. They slapped him with a $22.05 million qualifying offer for 2026.
Why? Because the underlying metrics say he's still elite. His 192 innings pitched proved his durability hasn't vanished. His strikeout-to-walk ratio remained respectable. Most importantly, that late-season bounce-back showed that his "stuff" is still there when his mechanics are in sync.
He's now a free agent, and while some teams might be scared off by the 4.83 ERA, the smart ones are looking at that 2.68 ERA from the final two months. Scott Boras, his agent, will undoubtedly be pointing that out in every meeting.
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What to Watch For Next
If you're tracking the zac gallen game log moving into next season, keep an eye on these three things:
- Fastball Location: Is he keeping the four-seamer at the top of the zone or is it leaking back over the heart of the plate?
- Sinker Usage: If he continues to use the sinker (around 10-15%), it takes the pressure off his four-seamer and helps him get those easy ground-ball outs.
- The First Inning: Gallen had a weird habit of giving up runs early in 2025. If he can settle in faster, those 5-run blowouts will disappear.
The 2025 season was a humbling one for Gallen, but it wasn't the end of his prime. It was a mid-career adjustment period. For a guy as smart as he is, expect the 2026 version to look a lot more like the 2023 All-Star than the guy who struggled through last June.
To get a true sense of his value, ignore the season-long ERA and focus on the innings and the strikeout gains he made late in the year. He's still a top-tier rotation piece for any team willing to look past a few bad months of home run luck. Check his velocity in his first three starts of 2026; if he's sitting 94-95 mph, the league is in trouble.