The Mariners rotation was arguably the best in the majors to begin the year, but has been one of the least productive over the past 20 games.
It’s been an inconsistent season so far for the Mariners, who started 8-13 but have since won four of six series and with the chance to make it five in seven with Sunday’s rubber match versus the White Sox. However, what’s concerning is the rotation specifically has gone in the opposite direction in beginning the 2026 campaign among the best in baseball, but recently performing poorly.
| Games | ERA | FIP | K/9 | BB/9 | WHIP | fWAR |
| 1-20 | 3.35 (7) | 2.93 (1) | 8.29 (17) | 1.98 (1) | 1.06 (4) | 3.2 (1) |
| 21-40 | 4.42 (20) | 4.60 (24) | 8.55 (9) | 2.77 (4) | 1.37 (21) | 0.8 (26) |
Understandably a lot of critics will put the majority of the blame on the rotation’s struggles at the feet of Luis Castillo, who is on course for the worst season of his 10 years in the majors. However, the reality is that everyone’s had their rough moments including even Bryan Woo, who is widely acknowledged as the staff ace.
In any event, the Mariners received some much needed positive news for the rotation on Saturday. Speaking ahead of the second game of the road series against the White Sox, manager Dan Wilson announced that Bryce Miller is now ready to come off the injured list.
Bryce Miller will make his season debut in Houston
Miller was placed on the 15-day injured list prior to the season with a left oblique strain, after only seeing 1.1 innings of action during spring training. However, following a rehab assignment which saw him pitch a couple of games in both A+ and Triple-A, the Mariners have clearly seen enough to bring him back into the fold.
The most recent rehab start saw Miller throw 61 pitches over 5.0 shutout innings on May 6 at High-A Everett, with him allowing a couple of walks and three walks while striking out two. He joined the team in Chicago with the Mariners and Wilson said: “Yeah, great to see him, and a chance to check in with him again and see how he’s doing.”
As for how Miller’s return impacts the setup, initially the Mariners will go with a six-man rotation as they navigated a schedule of 13 games in 13 games. The righty will make his first Major League start of the season on Wednesday, in the third of a four-game series in Houston versus the Astros.
Mariners going with a 6-man rotation is not a long-term solution
This approach does make sense at this stage, but a six-man rotation is not something which you would like to see the Mariners go with indefinitely. Aside from the fact such a setup leaves the bullpen a man down, they’re also currently without quality arms in Matt Brash, Gabe Speier and Carlos Vargas.
In fairness Wilson didn’t commit to the six-man rotation as a long-term solution, with the indication that the Mariners will review the situation once they return to Seattle following the Houston series. Earlier in the season the thinking was Emerson Hancock would be the odd-man out once Miller returned, but his improved form now muddies the waters somewhat.
On a surface level you would think Castillo should now be the man to move to the bullpen instead of Hancock, but it isn’t as straightforward as that. The three-time All-Star has been one of the stalwarts of the rotation since his trade from Cincinnati back in 2022, and his standing in the clubhouse means he should at least have some say in how he’s utilized in the coming months.
Luis Castillo just not his usual self so far in 2026
At the same time the Mariner can’t keep trotting Castillo out there in the rotation if he continues to struggle. He’s only made it through 6.0 innings twice in eight outings and one of those times was his first start of the season versus the Yankees, which doubled as his only quality start so far in 2026.
Another possibility includes Miller being the one who ends up moving to the bullpen. However, this seems unwise and unfair for a pitcher who led the rotation with the lowest ERA in 2024 and last season was the Mariners’ best starter during their playoff run.
In some respects the Mariners could consider this a good problem to have, but that loses some momentum if — for example — Castillo continues to struggle or Hancock doesn’t maintain his early-season form. In this respect, it will be interesting to see how the starters all do during this at least one go-round of a six-man rotation.
Photos courtesy of Tim Rogers Photography
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