With Bryce Miller coming back from the IL soon and top pitching prospects Kade Anderson and Ryan Sloan with their MLB debuts sooner than when many people may anticipate the Mariners rotation is in flux a little bit and today I’m going to talk about role changes for the foreseeable future.

Logan Gilbert / George Kirby / Bryan Woo

These three aces are awesome and their spots are secure.

Nothing to see here. Move along. Move along.

Bryce Miller

Bryce Miller will get his spot back in the rotation. He’s getting a near full IL rehab stint as an extended spring training because there’s no need to rush him back. This is the right thing to do and as he’s already brought back the velocity he should be good during the second half of the season. Now wouldn’t be a bad time to acquire Bryce Miller as the perception is down.

Luis Castillo

This season has been quite rough for Luis Castillo. In 28.1 innings following a blowup at the Twins he now carries a 6.35 ERA with a strikeout rate now below 20%. Since Castillo was traded to the Mariners he has seen his fastball velocity drop from 97.1 mph in 2022 to 94.8 mph this season and at the age of 33 his best days are likely behind him.

The other concern with Castillo has to do with his role on the team. Barring an actual injury to a starter, once Bryce Miller returns from the IL Castillo could be the first one on the chopping block. This is likely to take the form of either a phantom IL stint or a move to the bullpen. Regardless of the direction the Mariners choose to go either of these options will drastically lower his value even more. While I normally say don’t panic, I am selling Castillo at all costs in any formats except Ottoneu FGPT leagues or other formats that value long relievers.

Emerson Hancock

Many people were very quick to jump on board the Hancock bandwagon after his first start this year where he pitched six no-hit innings against Cleveland and those who did have been reaped the benefits. As someone who has watched a number of his starts on a nightly basis I was still more cautious than most and I wanted to see him do this over a stretch of at least 10-15 starts before I made any major changes to how I’m evaluating him. While these six starts have been awesome and he’s absolutely earned his spot in the Mariners rotation for as long as he can keep this up, my two concerns with Hancock are that regression in the past has tended to come quickly for him in the past and that he has benefited from some good luck so far this season.

The biggest problem I see is that Hancock is currently leaving 95.4% of runners on base which is simply unsustainable. For context, Freddy Peralta had the highest LOB% in 2025 among all qualified pitchers at 85.5% and Hancock is stranding nearly 10% more runners than Peralta. Hancock is also seeing a career high 12% barrel rate (a batted ball with a really good exit velocity and launch angle) and a career low .247 BABIP (batting average on balls in play) which also suggest that he could be benefiting from some good batted ball luck as well.

While Hancock’s arm angle drop has made some meaningful changes, I don’t think he will continue to pitch to a 2.86 ERA the rest of the way down the stretch. His expected ERA is currently 4.47 and I could absolutely see a world in which he finishes the season with an ERA in the range from 3.5 to 4.0. As for the playtime question, Hancock has earned his spot in the rotation right now but he’s going to have a shorter leash than most given the other starting pitchers in the Mariners rotation. What this means for me is that if someone else is willing to buy Hancock I’m ready to cash out now but if an offer’s not there I’m also happy to ride the wave out.

The prospects: Kade Anderson and Ryan Sloan

Both of these two prospects are absolute studs and the next two paragraphs are going to provide some basic context for each of the two.

Kade Anderson was the number three overall pick in the 2025 draft as a 6’2″ southpaw having won the 2025 college world series most outstanding player award. While he had Tommy John surgery in high school, he returned to become one of the most polished college arms available and right after the Mariners drafted him they shut him down for an extended off-season as they viewed building him up for a 162 game season is what he needed to be pitching in the majors rather than extra development.

The Mariners broke their traditional habits of going for college starters with Ryan Sloan in the second round of the 2024 draft and it certainly seems to be paying off here. Sloan is a 6’4″ righty who has praise for his makeup, work ethic, and an ability to repeat his delivery while pounding the strike zone. Throughout each level of the minors Sloan has answered every question he had and has excelled at a younger age than the competition.

It’s a massive green flag seeing how quickly both Kade and Sloan are being aggressively pushed closer to the majors, but their debuts could happen sooner than when many people may anticipate. Why am I saying this? Well all four of the Mariners homegrown starters were called up directly from Double-A Arkansas and skipped Triple-A Tacoma because they don’t like the extreme elevation challenges associated with the PCL venues and both Sloan and Kade are already pitching in Double-A.

When asked in early March if either of them would pitch at some point this year Mariners GM Justin Hollander said “I think they’re mature enough and their stuff is good enough. Whatever happens between the time they suit up (for a Mariners minor league) affiliate and the end of the season, a number of factors could come into play there. But I don’t see any reason why they couldn’t do it.”

The Mariners have always been super aggressive with promoting their top pitchers so I wouldn’t be surprised to see both of them called up sometime during the second half of this season. Kade and Sloan are studs and the Mariners will figure out a way to create a spot in the starting rotation specifically for them when they’re ready.

While it would be very expensive to acquire either of these prospects in a dynasty league right now I believe the price to acquire Kade and Sloan will skyrocket soon. Once word gets out about when one or the other may debut, the price to acquire Kade or Sloan will change from the cost of acquiring an elite prospect to the cost of acquiring an elite pitcher who could be a key player helping you win down the stretch this season and beyond. I’m trying to acquire Kade and Sloan on all fantasy baseball teams – even the win-now teams.

How will playtime shake out this season?

Having eight starting pitchers in a rotation is a very nice problem to have, but there’s a way the Mariners could address this. Luis Castillo could move to the bullpen. Once rosters expand the Mariners could employ a six-man rotation to ease workloads ahead of the playoffs. Hancock needs to continue pitching well over the full season. And then there’s always the injury bug (knock on wood). The Mariners will find a way to create space for all of their starters to help them down the stretch.

As for the postseason the Mariners currently have eight starters and five trusted relievers (Andres Munoz, Matt Brash, Gabe Speier, Jose Ferrer, and Eduard Bazardo). Between possible bullpen mini-breakouts from Cooper Criswell or Cole Wilcox and a strong likelihood of the Mariners acquiring a high leverage reliever or two at the deadline this will probably push Castillo off of the playoff roster.

What about trading a starter at the deadline?

While certainly not impossible, I would be a little surprised by this. Seattle is in a position to contend so any sort of swap would have to be a big leaguer for big leaguer trade. Luis Castillo would be the starter they would make available, but just like in the 2024-2025 off-season where nothing came to fruition the Mariners will still have a veteran player on a ~$20M/year contract which will deplete his value to other teams. They’re not going to salary dump him and having extra depth in the rotation isn’t a bad thing so while not impossible, there’s no incentive for the Mariners to trade him – especially when the Mariners already have a strong farm system and can add to the team without helping another contender.

Maybe… Hancock could be moved in season, but again this would require that another contending team would be willing to part ways with a good hitter. And the Mariners don’t need to deal from the big league team to fix their holes so why should they?