Luis Castillo's failing experiments are putting Mariners in a no-win situation

The most credit you can give Luis Castillo right now is that he's not trying the same things and expecting different results. The 33-year-old has made clear efforts to ward off Father Time. But for how much these aren't working, even his 6.35 ERA undersells it.

Castillo began his fifth season with the Mariners with six scoreless innings against the Yankees on March 30. He's allowed 24 runs over 22.1 innings in five starts since then, including seven runs over 5.0 innings in Minnesota on Monday night.

A constant throughout Castillo's career is that he hasn't performed well amid the cooler, wetter conditions that typically accompany March and April. As such, he was probably understating it when he described the especially cool and wet conditions at Target Field last night as "a little difficult."

And yet, the point when the Mariners would have to stop giving Castillo the benefit of the doubt had been out there for a while. He was their ace in 2022 and 2023. He was then more like an average-ish pitcher in 2024 and 2025, with warning signs that his prime was was on borrowed time. Now in 2026, those warning signs have compounded into a message: It's too late.

Luis Castillo's velocity and pitch mix point to an aging pitcher fighting a losing battle

Back in spring training, Castillo had Mariners camp atwitter over his offseason efforts to regain some of the velocity he had lost. And it seemed to work, as he averaged 95.0 mph on his four-seamer after averaging just 93.9 mph the previous spring.

Cut to now, though, and the 94.8 mph he's averaging on the heater is the exact same as his average from the first month of last season. "At least he's not losing velocity" is the only positive way to spin that, and the .556 slugging percentage against his four-seamer obliterates whatever comfort there is to find in that sentiment.

Even Castillo sees the writing on the wall. Whereas he was reluctant to throw his fastball less often in 2025, his usage of it is down from 46.3 percent to 40.7 percent. He's throwing more sliders, which is a solid idea being badly executed. The pitch has only a 32.4 whiff percentage and has been hit for a .310 average and a .517 slugging percentage.

There are only so many ways Castillo can go from here. Maybe try more sinkers. Or, more sinkers and more changeups. But since those two pitches have also gotten hit hard, his fundamental problem is unavoidable. It's not how he's using his stuff, but rather the stuff itself.

If all things were equal, Castillo would be the obvious man out when Bryce Miller is ready to come off the injured list. But it's obviously not that simple. He's a three-time All-Star who is owed $24.15 million this year and the next. It's hard to move a guy like that to the bullpen.

The only other options are to find an excuse to put Castillo on the IL or to just move on from him. They could either designate him for assignment to try to trade him. But both processes would almost certainly have the same outcome of the Mariners eating a lot of money. The only way they're dealing him is if they pay out his remaining salary or take back comparable money in a bad contract swap.

So yeah, it's bad options all the way down. The only way the Mariners could have avoided this is by trading Castillo earlier, but to say they should have done so requires ignoring how he was still a productive member of good teams even as he was clearly declining. Choosing to ride that train out to its natural end was never a bad call.

All the same, it sure seems like the end has arrived. The only question now is exactly how the Mariners want to cut their losses.

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