George Kirby’s New Four-Seam Fastball Experiment Boosts 2024 Outlook

This article takes a closer look at the wild ride that was George Kirby‘s 2025 season with the Seattle Mariners. We’ll poke around at the injuries, pitching tweaks, and maybe a bit of plain old bad luck that all piled up to make this year a real head-scratcher for a guy who usually makes pitching look easy.

George Kirby’s Uncharacteristic 2025: A Deep Dive into Pitching Puzzles

For quite a while, George Kirby stood out as the Mariners’ rock-steady arm. He built his reputation on control and forcing hitters into weak contact, thriving in Seattle’s pitcher-friendly park.

Fans loved him for it. Fantasy managers did too.

Injuries Strike: The Unraveling of a Promising Season

But then 2025 happened, and the script flipped. Kirby’s year got derailed by shoulder inflammation and a nagging knee issue.

He landed on the MLB injured list for the first time in his career. That was a big deal for someone who’d always been so dependable.

When he came back, you could tell he wasn’t quite himself. There were flashes of dominance, like that stretch against the Angels, but the overall vibe was off.

He wrapped up 2025 with a 4.64 ERA and a 3.58 FIP over 106.2 innings. For Kirby, that’s a step down from his usual high standard.

The Paradox of Kirby’s Pitching Adjustments

Trying to get back on track, Kirby started tinkering on the mound. Whether he meant to or not, he changed his approach, and the stats got weird.

Out-of-Zone Command and the Strikeout Surge

He started throwing more pitches outside the strike zone. That’s not what you’d expect from a guy known for laser-sharp command, but it’s what happened.

His walk rate jumped to 5.5%, the highest of his career. Still, he managed to stay among the league leaders at limiting walks, which says something about his raw skill.

Oddly enough, moving away from the middle of the plate led to more strikeouts. He posted his best called-strike-plus-whiff rate ever.

So even though he threw more balls, hitters kept swinging and missing, or just watching strikes go by. That’s got to be frustrating if you’re in the batter’s box.

• Increased pitches outside the zone
• Highest career walk rate (5.5%)
• Still elite in limiting walks
• Uptick in strikeouts
• Best career called-strike-plus-whiff rate

But there was a catch. More whiffs came with more barrels—opponents started squaring him up more often.

Was that because of the injuries? Maybe rust from the IL? Or did Kirby just decide to gamble a little more with his pitch locations? Hard to say for sure.

The Blurring of Pitches and the Role of Luck

Those injuries didn’t just mess with his stats—they messed with his pitches too. Kirby pretty much ditched his splitter and threw fewer changeups, saying he didn’t feel right after coming back.

He also dropped his arm slot, maybe without realizing it, which changed how his sinker moved. That tweak blurred the lines between his breaking pitches, making them less distinct.

ERA-minus-FIP Differential: Unpacking the Misfortune

Kirby’s season got even trickier with his 0.85 ERA-minus-FIP differential. That number measures the gap between a pitcher’s Earned Run Average (ERA) and Fielding Independent Pitching (FIP).

It was the worst for any Seattle starter with a similar workload in the past decade. When this differential is high and positive, it usually means a pitcher ran into some bad luck—or maybe the defense behind him just wasn’t up to par.

Defensive issues definitely factored in, but they don’t tell the whole story. Mistakes that might’ve led to an out or a harmless single before turned into louder contact, with hitters cashing in for extra bases and runs.

It seems like a mix of misfortune and a slightly weaker knack for wriggling out of jams. In past years, Kirby often escaped those spots, but this season, things just didn’t break his way as often.

Heading into 2026, you can feel some real determination around George Kirby. He wants to go back to his old pitch mix, maybe bring back that nasty splitter, and use last year’s struggles as motivation.

He’s aiming to regain his ace status and show off the focused, dominant pitching Mariners fans love. If anyone can pull it off, it’s probably Kirby.

 
Here is the source article for this story: 40 in 40: George Kirby tried something new