Mariners Preview: Starting Rotation
Seattle will go as far as the starting staff can take it in 2026.
After being baseball’s best starting rotation in 2024, Seattle’s staff took a step back last year. Not a freefall by any measure. But a noticeable drop off, nonetheless.
In 2024, the Mariners led MLB by a large margin with 92 quality starts - just three shy of the club record set in 1990. But last year, the rotation’s 67 quality starts were seventh-best. Good, but not great compared to the previous campaign.
Across the board, a statistical decline from one year to the next was evident. Respectable in most categories, but not the world-busters of 2024.
Two years ago, the Mariners had an MLB-leading four pitchers with 30-plus starts -Luis M. Castillo, Logan Gilbert, George Kirby, and Bryce Miller. However, just Castillo and Bryan Woo reached 30 starts this past season.
Gilbert, Kirby, and Miller spent time on the IL due to arm-related injuries, reducing their availability and, at times, their effectiveness.
Rotation Injuries (2025)
Bryce Miller (Elbow inflammation) - 92 lost days
George Kirby (Shoulder inflammation) - 59 days
Logan Gilbert (Elbow flexor) - 51 days
Bryan Woo (Pectoral strain) - 10 days*
* Final 10 days of season
It’s worth noting a pectoral injury cost Woo the final week of the regular season. The issue subsequently limited the 26-year-old to just two relief appearances in the ALCS.
Emerson Hancock and Logan Evans primarily covered for Gilbert, Kirby, and Miller during their absences. Luis F. Castillo and Casey Legumina also combined for three starts.
Starts in 2025
Luis M. Castillo (32)
Bryan Woo (30)
Logan Gilbert (25)
George Kirby (23)
Bryce Miller (18)
Emerson Hancock (16)
Logan Evans (15)
Luis F. Castillo (2)
Casey Legumina (1)
The combined season numbers of Hancock and Evans essentially amounted to one below-average starter. Not terrible, but not nearly on the same level as the pitchers they subbed for.
Despite the difficulties we’ve discussed, Seattle’s best starters managed to have respectable seasons. Four Mariners were top-50 in Expected Weighted On-base Average (xwOBA), which is a Statcast product derived from quality of contact allowed. So unlike ERA, defense (good or bad) does not influence xwOBA.
xwOBA of M’s Starters with MLB rank*
Bryan Woo (.274) - 8th in MLB
Logan Gilbert (.275) - 9th
George Kirby (.306) - 34th
Luis Castillo (.312) - 46th
Logan Evans (.350) - n/a
Bryce Miller (.351) - n/a
Emerson Hancock (.360) - n/a
MLB Average for SP’s = .320
* 500-batter minimum
Even though the rotation dealt with injuries most of the season, a segment of Mariners Twitter wanted the team to trade a starter over the winter to bolster the offense. Fortunately, the front office kept the gang together. Let’s discuss where the staff stands at the moment.
Current events
The master plan has already hit a snag. Miller is recovering from an oblique strain, which means he’ll start the season on the IL. The injury probably isn’t a long-term issue, which is good news.
Evans isn’t an option to replace Miller since the 24-year-old is out for the year after undergoing Tommy John surgery. The top candidates to take Miller’s spot are Hancock and Cooper Criswell.
Starter pool (2025 xwOBA)
Logan Gilbert (.275)
George Kirby (.306)
Luis Castillo (.312)
Bryan Woo (.275)
Bryce Miller (.351)*
Emerson Hancock (.360)
Cooper Criswell (MiLB)
Blas Castaño (MiLB)
Jhonathan Díaz (MiLB)+
Casey Lawrence (MiLB)+
Ryan Sloan (MiLB )+
Kade Anderson (NCAA)+
Randy Dobnak (MiLB)+
Dane Dunning (MiLB)+
Gabe Mosser (MiLB)+
Michael Morales (MiLB)+
Teddy McGraw (MiLB)+
Logan Evans (.355)*
+ Not on 40-man roster
* Injured
Hancock has experience being a rotation replacement at the beginning of a season. He’s done it the last two years when a starter went to the IL before Opening Day. The following illustrates his numbers from 2025, which were suboptimal.
Criswell made just seven appearances with Boston in 2025 spending most of the season with Class-AAA Worcester. But the righty did have a 3.49 ERA and a .319 xwOBA when he made 18 starts with the Sawx two seasons ago.
Something worth noting: Criswell’s 51.6-percent ground ball rate in 2024 was 10th highest among starters with 70 innings. A small sample that aligns with a career 49.8-percent rate generated during parts of five seasons and 154 big-league innings.
One last note regarding the first wave of replacements. Criswell doesn’t have a minor-league option. Therefore, he’d have to clear waivers before being assigned to Class-AAA Tacoma. Conversely, Hancock does have an option remaining. This may factor into who the Mariners’ select for the Opening Day rotation and bullpen.
As for Gilbert and Kirby, both are in their prime. There’s no reason to expect their effectiveness to diminish this year, as long as they avoid the IL. On the other hand, the stats of Castillo are hinting age-related regression is under way. That said, the 33-year-old was the only Seattle pitcher to make every start in 2025. Availability matters, too.
The other guys
I suspect the second wave of replacements would be names from the starter pool listed above, assuming they’re still with the organization once the season begins. We’ve seen Blas Castaño, Jhonathan Díaz, and Casey Lawrence appear with the Mariners in various roles before. Usually for short durations.
As for options down on the farm, Ryan Sloan and Kade Anderson are the names most often mentioned by the media and fans. And let’s face it, their potential was the reason some fans were willing to deal a starter in the offseason. Still, both youngsters are light on professional experience - particularly Anderson.
In his first season after college, Sloan logged 82 frames with Class-A Modesto and High-A Everett. But it’s important to recognize the right-hander pitched every seven days. Clearly, the organization was closely managing the development and workload of the top pitching prospect.
In the case of Anderson, his next pitch in a regular season game will be the first of the 21-year-old’s professional career. I suspect the Mariners ramp up last year’s third overall pick in the same manner it did with Sloan.
Am I suggesting Sloan and Anderson can’t or won’t help the Mariners this year? No. But expecting these young and inexperienced arms to appear with the club early in the season seems unrealistic. Can I envision either or both pitching with Seattle in September? Assuming they remain healthy and continue developing in the minors, definitely.
Outlook
Last season serves as a reminder that nothing is certain when it comes to starting pitching, which is baseball’s most valuable commodity. But as things sit today, the rotation is in good shape.
Everyone except Miller is ready and he likely returns early in the season. If the rest of the gang stays available and effective, the Mariners’ postseason outlook is very promising.
My Oh My…