Mariners' Luis Castillo decision feels like the beginning of the end for fallen ace

At this point, Luis Castillo has pitched about as many innings for the Mariners (664.2) as he did for the Reds (792.1). He was a major deadline acquisition for Seattle in their 2022 playoff push and helped his new team end a postseason drought that lasted decades.

In the years since, he has been a consistent piece of the Mariners' rotation, never posting an ERA higher than 3.64 and giving Seattle at least 175 innings in each of his three full seasons. However, 2026 has come with its fair share of struggles and the organization's most recent roster move suggests that his time as a starter is drawing to a close.

The Mariners are officially moving Luis Castillo out of the rotation and into the bullpen

Seattle recently made a flurry of roster moves and another change they also announced was that Castillo would be serving as a long reliever behind Bryce Miller as the latter continues to ramp up following his recent return from the injured list.

Just two seasons ago, Castillo was the Mariners' trusty ace and Opening Day starter. Just last season, he remained a solid part of the pitching staff, posting a 3.54 ERA and 3.88 FIP, but this year, things have gone off the rails. He has a 6.41 ERA over 46.1 innings and his most recent outing directly resulted in a loss.

With diminished stuff across the board, especially in the later innings, a decreased innings workload seems like a prudent decision, but it seems like deeper-rooted issues are quickly making him a less viable pitcher. His fastball has been hammered this year, with opposing hitters batting .307 and slugging .573 against the pitch.

While it's never an ideal situation to see a player decline so quickly, this may actually work out in Seattle's favor, at least for now. There were some questions about who would cede their place in the rotation for Bryce Miller upon his return, especially since Emerson Hancock has continued to pitch well, but Castillo has made the answer much clearer.

If Hancock does begin to regress as his numbers suggest, then it could also give the Mariners an opportunity to call up Kade Anderson, who has already seemed ready for a tougher challenge in his first professional season.

Castillo has another year on his contract and a vesting option that depends on time injured between 2025 and 2027 as well as his innings pitched in 2027. The way things are currently going, it seems doubtful that he'll remain on the roster long enough for that to be a real consideration for the organization.

His contributions over the past few years are very much appreciated but in the sport of baseball, the question at hand is always "what have you done for me lately" and for Castillo, the answer is unfortunately not much.

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