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Castillo will make his White Sox debut Thursday in Boston, James Fegan of SoxMachine.com reports.
After making his final start for the Mariners on Tuesday before being dealt to the White Sox on Saturday, Castillo will be well-rested and will have some extra time to get acclimated before debuting for his new organization. A three-time All-Star, Castillo brings ample experience to the White Sox rotation, but he submitted a 5.06 ERA and 1.39 WHIP -- both career-worst marks -- over 99.2 innings for the Mariners this season. He's been especially stung by the long ball recently, surrendering seven home runs over his last three outings after giving up just two total in his eight appearances before that.
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White Sox's Luis Castillo: Moving on to White Sox
Rotowire
The White Sox acquired Castillo from the Mariners on Saturday in exchange for right-hander Seranthony Dominguez, outfielder Nolan Jones and catcher Boston Smith, Jeff Passan of ESPN.com reports.
The 31-year-old righty will head to Chicago and bolster a rotation that's received excellent results from Davis Martin and Sean Burke but uneven production from Anthony Kay, Noah Schultz and Erick Fedde at the other three spots. While the three-time All-Star easily becomes the White Sox's most battle-tested starter, Castillo has endured a career-worst 2026 campaign. After submitting a 3.54 ERA and 1.18 WHIP in 32 starts for Seattle a season ago, Castillo turned in a 5.06 ERA and 1.39 WHIP in 20 appearances (17 starts) in 2026 prior to being dealt. Castillo showed signs of righting the ship in May and June, but he went 0-3 with a 5.48 ERA and 1.52 WHIP while serving up seven home runs in 23 innings over four July outings. He last pitched Tuesday, so Castillo could be ready to make his White Sox debut during the team's series in Boston early next week.
Mariners' Luis Castillo: Gives up five runs against Dodgers
Rotowire
Castillo allowed five runs on 11 hits and two walks while striking out two over five innings in a no-decision versus the Dodgers on Tuesday.
Castillo gave up multiple home runs for the third start in a row, as Shohei Ohtani led off the bottom of the first inning with a long ball and Max Muncy went yard in the fifth. This was the first time Castillo had allowed five earned runs since April. July was a rough month for the veteran, who gave up 14 runs over 23 innings across his four outings. On the year, he has a 5.06 ERA, 1.39 WHIP and 86:32 K:BB across 99.2 innings over 20 games (17 starts). Castillo is tentatively projected to make his next start at home versus the Tigers, but that is a loose projection given the likelihood the Mariners move a pitcher before the trade deadline.
Mariners' Luis Castillo: Works seven innings in loss
Rotowire
Castillo (3-9) allowed three runs on four hits and two walks while striking out three over seven innings to take the loss Tuesday versus the Reds.
Two of the four hits Castillo allowed were solo home runs, though it was Sal Stewart's sacrifice fly in the fifth inning that ultimately sealed the loss for Seattle. This was a third straight defeat for Castillo, who has allowed nine runs over 18 innings with an 11:4 K:BB in that span. For the season, he has a 4.85 ERA, 1.33 WHIP and 84:30 K:BB through 94.2 innings across 19 appearances (16 starts). Castillo is tentatively lined up for a tough road start versus the Dodgers next week, though he is a candidate to be traded if the Mariners want to clear their logjam of starters.
Castillo (3-8) took the loss Friday against the Rays, allowing four runs on nine hits and a walk while striking out four batters across five innings.
Castillo allowed three homers and has dropped three of his last five starts. However, the veteran hurler has given up two or fewer runs in seven of his last nine outings, so he's been pitching well lately, all things considered. Castillo saw his season ERA rise to 4.93 after this start, but he has a more respectable 3.90 ERA in six starts and 32.1 innings since the beginning of June.
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Mariners' Luis Castillo: Earns quality start in loss
Rotowire
Castillo (3-7) allowed two runs on five hits and a walk while striking out four over six innings to take the loss versus the Blue Jays on Friday.
Castillo was mostly fine, but he allowed both runs and four of the five hits on his line during the third inning. The Mariners mustered just six baserunners in the game, giving Castillo virtually no support. He has posted back-to-back quality starts but still has just one win in his last five outings. Castillo is at a 4.79 ERA, 1.33 WHIP and 77:27 K:BB through 82.2 innings over 17 games (14 starts) this season. The veteran right-hander is tentatively projected for a road start in Miami next week.
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Mariners' Luis Castillo: Quality start in win
Rotowire
Castillo (3-6) earned the win against the Guardians on Friday, giving up one earned run on four hits and a walk while striking out four batters across six innings.
A first-inning RBI double from Kahlil Watson gave the Guardians an early 1-0 lead, but that ended up being the only run Cleveland would score against Castillo, who allowed just three additional baserunners before departing the game after six innings. Friday marked the 33-year-old's first win since the end of May, as well as his first quality start since his season debut March 30. He'll take a 4.93 ERA and 1.36 WHIP into his next start against the Angels, who have turned in a .758 OPS since the beginning of June.
Mariners' Luis Castillo: Roughed up in relief outing
Rotowire
Castillo allowed five runs (four earned) on seven hits and struck out four without walking a batter over four innings of relief in Friday's 6-2 loss to the Red Sox.
Castillo wasn't tagged with the loss, as that went to Bryce Miller. The Mariners' offense didn't give much support to either pitcher, but Castillo didn't do his part to keep the game close after a four-run seventh inning. He has now allowed 11 runs (seven earned) across 15.1 innings in June. Both Castillo and Miller are expected to work in traditional starts at some point during the Mariners' six-game road trip next week.
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