Luis Castillo’s Disturbing Spring Trend Is Hard for Mariners to Dismiss

We probably need to stop doing the polite spring-training thing with Luis Castillo. The usual veteran-working-on-things caveats can be true. But there’s a difference between a messy spring line you can laugh off and a spring line that starts poking at concerns already sitting in the back of your mind.

Castillo’s spring has drifted into that second category. He’s made four Cactus League appearances and owns a 10.80 ERA with a 2.20 WHIP over 10 innings, and that alone is ugly enough. The part that makes it harder to wave away is how it lines up with some of the broader trends from last season.

Mariners Cannot Ignore What Luis Castillo’s Spring Is Starting to Reveal

That makes this conversation uncomfortable for Mariners fans. Castillo is still supposed to be one of the anchors of the rotation, the veteran who settles everything down. They call him The Rock for a reason. Lately, though, The Rock has been getting rocked. In his most recent spring outing against San Diego on March 17, he worked four innings and gave up five hits, two of them solo home runs, while striking out one and walking one. That’s not catastrophic on its own, but it’s also not exactly the kind of tune-up that calms anybody down.

Bogey makes it back-to-back! pic.twitter.com/5qlJJI4vBy
— San Diego Padres (@Padres) March 17, 2026

To be fair, Castillo was still a useful and often good starter in 2025. He made 32 starts, posted a 3.54 ERA, and threw 180 2/3 innings with 162 strikeouts. That is a valuable pitcher. The problem is that the version of Castillo the Mariners really need is not merely useful. It is the one that can still feel like an ace on the right night.

And the indicators from last season suggested that version was becoming a little harder to find. His strikeout rate fell to 21.7 percent in 2025 after sitting at 24.3 percent in 2024 and 27.3 percent in 2023, while opponents also made louder contact against him than they used to. His 46.4 percent hard-hit rate was one of the worst marks of his career and ranked near the bottom of the league.

That’s where the pitch-mix conversation starts to appear. Castillo threw his four-seamer 46.4 percent of the time in 2025 and his sinker another 22.1 percent, while the slider sat at 20.3 percent and the changeup dropped to just 11.2 percent. For a pitcher whose changeup used to be one of the nastiest disruptors in his arsenal, that’s nothing to sneeze at.

It feels like the whole story. The fastball can still play, but it is a lot harder to live that way when the velocity margin is not what it used to be. Castillo averaged 95.0 mph on his four-seamer in his Feb. 27 spring debut against Arizona, almost identical to his 2025 average, but that also fits the longer trend line of a gradual drop from the upper-97 range he showed earlier in his career.

And that is really the concern here. This is not just about one bad spring ERA. It is about whether the Mariners are watching the same contact-quality problem from 2025 show up again before the games even count.

Maybe this all looks silly in three weeks, and Castillo flips the switch once the regular season starts, reminding everyone why he has carried this staff so often. Mariners fans would love that version of the story. But pretending there is nothing to monitor here feels a little too convenient right now. Spring training may not tell the whole truth, but with Castillo, it is starting to repeat a truth Seattle has already seen before.