A platoon in the Mariners' rotation? Well, kind of ...

This story was excerpted from the Mariners Beat newsletter. This edition was written by MLB.com reporter Jackson Stone. To read the full newsletter, click here. And subscribe to get it regularly in your inbox.

CHICAGO -- Mariners starters are in a unique situation this upcoming week as they prepare to be a part of a six-man rotation -- at least for the time being.

The prevailing thought is that after this first time through, Bryce Miller -- who is expected to return from the injured list Wednesday and start in Houston -- will piggyback with the struggling Luis Castillo so that Seattle can pitch Bryan Woo, George Kirby and Logan Gilbert as much as possible every five games.

It’s a situation that is still very fluid, and it can change depending on the health and performance of Miller and Castillo over their next couple starts.

The thing every team desires -- healthy and capable starting pitching -- has turned into a bit of a problem in Seattle. But that, too, can always change in an instant.

“We obviously have a privilege of having the surplus of starting staff talent that we do,” said Woo, who is slated to go Tuesday. “It’s never an easy decision or whatever with logistics, but one way or another we are just happy that everyone’s healthy and getting back. We just want to see guys in the field competing, and I think everyone’s so selfless to the point that we just want to support the next guy and see them do well. No one really cares about what order, or who’s No. 1 or whatever; we just want to see the next guy do that.”

The only reason this is a conversation is because Emerson Hancock, who took over Miller’s rotation spot while he was out with an oblique injury, has taken off with his opportunity. The 26-year-old righty has pitched to a 3.21 ERA in eight starts, including a 14-strikeout gem against the Royals.

“It’s fun to watch Emerson come into his own this year and have his own success as a starter,” said Miller, who had a 1.98 ERA in four rehab starts. “Having six guys is definitely a blessing. A lot of guys are really struggling. You look at Houston and they’ve had what, 12 starters already? You can never have too much pitching. As soon as you think you do, something happens and then you’re down. It’s a really deep group, and I think we have fun building off each other.”

Castillo's struggles have also complicated issues with the rotation. The Mariners don’t want to move their highest paid player and one of the most respected voices in the clubhouse to the bullpen. The veteran has made 251 Major League appearances, all starts, and has been the workhorse for Seattle the past five seasons. Castillo hasn’t been his usual self so far, but the Mariners want both him and Miller to stay stretched out in case of another starter injury -- which would end this six-man plan altogether.

The downside is pitching Woo, Gilbert and Kirby less -- at least for the time being before the Mariners decide if piggybacking Castillo and Miller could be a permanent option moving forward. The extra rest is also inconsistent with how it impacts performance levels for each starter. Woo, for example, has a higher ERA (4.98) when on six or more days of rest compared to four days (2.90) or five days (3.00). But Miller has a lower ERA (3.46) on six or more days rest than any other amount of time off. Granted, the sample sizes for each type of start vary, and six or more days of rest happen with less frequency.

“At the end of the day, I usually throw a bullpen on day three, even if we are on a five-, six- or seven-day [break],” Miller said. “… It’s funny, in college on seven days' rest, it felt like it was a stretch to be ready, and now it’s like seven days feels like forever.”

The one thing the Mariners can say for certain is they are happy to have Miller back, in whatever capacity. The righty had an impressive 2.94 ERA across 31 starts in 2024 before three strong starts in the '25 postseason had him primed to be a major player in the rotation in 2026.

“Watching the guys go out and compete, watching from the couch wasn’t fun, but I’m ready to go,” Miller said. “Ready to build off the postseason momentum I had and I think all my stuff’s been up a little bit. Velo’s been up the whole year so far. I’ll be on a seven-day [break] coming into Houston, so I should be feeling good.”

And that’s the positive. It’s only May, but any innings you can take off a starter as the team works toward another deep postseason run is a good thing. The Mariners (19-22) need to play better to get to that point, but with a starting staff that entered Sunday leading the league in innings pitched (229), finding a way to get an extra off-day -- even for just one turn through the rotation -- can be helpful.

“The most important thing is obviously staying healthy, but also just being ready for postseason baseball,” Woo said. “If that means taking some innings off guys early on -- and making sure that everyone is taking care of themselves and doing the right things throughout the year so that we’re ready at the right times -- I think that’s the most important thing. Trying to get to a certain innings limit or workload, it’s great and we all want to pride ourselves in being workhorses, but also there’s a balance to it of doing what’s most important and impactful for the team as well.”