Mariners trade deadline intel should revive a controversial Luis Castillo idea

For a while now, trading Luis Castillo has loomed as a solution to multiple problems for the Seattle Mariners. It would do away with his contract, for one. Arguably even better, it would clear a spot for Kade Anderson in the starting rotation.

It takes two to tango, however, and the latest from Ken Rosenthal and Will Sammon of The Athletic is that other teams "likely are reluctant" to trade for the 33-year-old Castillo. It's because of his contract, which owes him $24.15 million this year and in 2027, with a $25 million vesting option for 2028.

Instead, Rosenthal's and Sammon's report puts Emerson Hancock on the table as the starter who might be most likely to leave Seattle. And that's fine, so long as the return is a right-handed hitter who could help both in 2026 and beyond.

A trade wouldn't necessarily solve the Mariners' rotation logjam on its own

Yet even if it's Hancock who goes and Castillo who stays, the Mariners would still have a major decision to make on what to do with their starting rotation.

One option would be to not fill Hancock's spot and shift to a five-man rotation, but that would mean keeping Anderson down in the minor leagues. He deserves better. Keith Law of The Athletic even has him ranked as MLB's No. 1 prospect, positing that the lefty would be in "27 or 28" other rotations right now.

Another option would be to call up Anderson and keep him and Castillo in a six-man rotation with Logan Gilbert, George Kirby, Bryan Woo and Bryce Miller. But that would mean doubling down on the six-man rotation instead of reckoning with its drawbacks. It means less action for the best starters, and not necessarily less work for a bullpen with one less arm in it.

Thus, a modest proposal: Put Castillo in the bullpen.

Luis Castillo might be exactly the high-leverage reliever the Mariners need

This is a concept that we pitched way back in early May, when it was strictly theoretical. Castillo was struggling as a starter at the time, but his times-through-the-order and pitch count splits suggested he could be effective in shorter spurts.

Small sample size and all, but the three appearances he made out of the pen as part of the short-lived piggyback experiment ultimately support the notion that he can, in fact, be useful in relief. He has a higher ERA as a reliever (5.56) than as a starter (4.75), but with a lower WHIP, a higher K/9 and a lower OPS.

Plus, the velocity on his fastball ticked up about as much as you'd expect:

Look, nobody would expect Castillo to become Mason Miller. But there's enough ceiling for him to emerge as some kind of leverage reliever, which points to a scenario in which the Mariners solve their bothersome bullpen issues entirely with in-house options. Instead of a trade, it might only need a converted Castillo and healthy versions of Matt Brash, Carlos Vargas and Cooper Criswell.

It's not how the Mariners want to be using a $24.15 million pitcher, to be sure. But at the very least, moving Castillo to the pen would be a pivot away from what the Mariners have been doing. And since what they've been doing hasn't worked, it should be on the table just on that account.

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