Despite countless rumors over the years, the Mariners have long been resistant to the idea of trading from their strong rotation. The stance looks to continue at this year’s deadline, as Adam Jude of the Seattle Times writes that the M’s “have given no indication they are willing to move any of their top five starting pitchers this summer.” That being said, Jude speculates that “come July…Luis Castillo’s name figures to resurface in trade chatter.”
The caveat underlines the fact that Castillo is simply no longer viewed as one of the Mariners’ best rotation options. This was reflected when Castillo was twice used as a piggyback starter behind Bryce Miller once Miller returned from a season-opening stint on the 15-day injured list. Emerson Hancock pitched so well in Miller’s regular rotation spot that the M’s kept him on a regular turn, and instead opted for the piggyback strategy on a temporary basis. This didn’t entirely sit well with Miller or Castillo, but the Mariners then moved to a six-man rotation that they’ll employ until the middle of June, once the club is through a busy stretch of the schedule.
It remains to be seen how the M’s will re-adjust back to a five-man rotation at that point, particularly since Castillo has looked a little more like his old self after a rough start to the season. Castillo has allowed one earned run over his last nine innings of work, though his ERA still sits at 5.53 over 55 1/3 total frames. Castillo’s 4.08 SIERA is much more palatable and his walk and strikeout rates are around league average, but the veteran right-hander has also allowed a ton of hard contact.
Most teams would be more than satisfied with this sort of production from a back-end starter, yet Seattle is in the enviable position of having too many starters for too few rotation slots. Beyond Hancock’s breakout, George Kirby, Logan Gilbert, and Bryan Woo are all pitching well, and Miller has looked tremendous since his return. If this wasn’t enough starting depth, the M’s have a few starters (i.e. Dane Dunning, Randy Dobnak, Jhonathan Diaz, Casey Lawrence) with MLB experience down at Triple-A Tacoma, plus there has been speculation that top prospect Kade Anderson could go from Double-A to the majors before 2026 is over.
Dipping too far down the depth chart has never held much appeal for the Mariners, however, though Hancock’s emergence has been a big help on that front. The “you can never have enough pitching” mantra rings especially loudly for a team aiming to make a World Series run, so the M’s would be hesitant to move even Castillo unless they were sure they had enough starting pitching to cover a lot of extra postseason innings.
Castillo’s contract is another reason why the veteran has been the starter the Mariners have at least been open to moving, even as rival teams have surely asked more about the younger and more controllable arms. Castillo is owed roughly $14.6MM for the remainder of the 2026 season, $22.75MM in 2027, and a $25MM option for 2028 will vest if Castillo pitches at least 180 innings in 2027 and finishes the season healthy.
The no-trade protection that existed in Castillo’s extension is now up, so he can be dealt without his approval. That removes one potential obstacle to a deal, though the price tag remains steep for a 33-year-old pitcher who might be a mid-rotation starter at best at this stage of his career. Seattle probably doesn’t have interest in eating much or any of Castillo’s salary, and trading Castillo for another player with a hefty contract only has limited appeal, unless the M’s felt this hypothetical player would help will another need (probably on offense).
