White Sox Found the Key to Unlocking Luis Castillo

When the Chicago White Sox traded for right-handed pitcher Luis Castillo at the MLB trade deadline, they knew the upside that was still there with the three-time All-Star and 10-year MLB veteran.

Sure, Castillo had posted a 5.06 ERA with the Mariners on the season, by far the worst mark of his career. But a 3.88 ERA in 10 starts prior to the deadline indicated that Castillo was starting to return to form. Not to mention the fact that the White Sox identified a key issue with his pitch usage that could help bring back his best stuff.

Go back a handful of years, and Castillo's changeup was his most-used pitch. But over time, it's an offering that Castillo has started to abandon. An odd choice, considering it's been his highest-rated pitch in Stuff+ metrics over the last four seasons.

Still, the White Sox have done a nice job of identifying how Castillo can improve, and it's been clear that reviving the changeup is a big part of their plan for how Chicago intends to get production from Castillo in 2026 and beyond. Let's not forget that a big part of that deal with the Mariners was Castillo's contract control, which keeps him with the White Sox through 2027 and gives them a vesting option for 2028.

When Castillo took the ball against the Boston Red Sox in his White Sox debut, I liked what I saw, even if the results in the box score didn't match. Castillo went four innings, surrendering six hits and five earned runs, with five strikeouts. But the eye test told a different story. Boston recorded a lot of soft contact that resulted in hits due to batted-ball luck. The ball just wasn't bouncing Castillo's way. Though the stuff and control seemed to be as advertised.

Those suspicions were confirmed on Wednesday night when Castillo took the ball against the Cincinnati Reds, one of his former teams, and delivered one of the best pitching performances the White Sox have had all year.

Castillo went seven scoreless innings with just one hit, two walks, and 10 strikeouts. He threw 104 pitches on the day, getting the White Sox deep into the ballgame and recording the win. Of those 104 pitches, he threw 20 changeups. All 20 of them were thrown to left-handed batters, collecting eight swings and misses and two called strikes.

Castillo recorded 22 total whiffs in the ballgame.

That's the pitcher the White Sox traded for. A dominant primary fastball complemented by a nasty changeup deployed against left-handed batters to create swings and misses with two strikes. A guy who can throw over 100 pitches, get you seven-plus innings of work, and give you a chance to win the ballgame each time he takes the mound.

Seven scoreless with double-digit strikeouts is probably a bit of an outlier, but I do think this is more the pitcher that we're going to see Castillo be for the home stretch of 2026. And if that's the case, it'll be a tremendous job by the White Sox front office and player development staff to identify a three-time All-Star and quickly recognize what he needs to do to return to form.