Luis Castillo Traded to White Sox, Bolsters Rotation
The Chicago White Sox have made a significant move ahead of the trade deadline, acquiring veteran right-handed starting pitcher Luis Castillo from the Seattle Mariners in exchange for right-handed reliever Seranthony Domínguez, outfielder Nolan Jones, and catcher prospect Boston Smith.
Castillo, 33, has had a mixed season, with a current Fielding Independent Pitching (FIP) of 4.57, a career-worst mark. However, he has a strong overall body of work, boasting a career ERA+ of 115 and three All-Star selections across parts of 10 MLB seasons. In 2025, he had a 108 ERA+ and a sub-4.00 FIP in 32 starts. Castillo has topped 30 starts in each of the last three seasons.
The White Sox had been seeking to bolster their rotation ahead of Monday’s trade deadline as they attempt to maintain their lead in the American League Central. Castillo is under contract through the 2027 season with a vesting option for 2028 in his contract.
On the other hand, the Mariners will save a significant chunk of change, with Castillo’s salary set to increase in the coming years. The team had been expected to deal from their rotation depth to address roster needs elsewhere.
Breakdown of the Trade
The White Sox will absorb the entirety of Castillo’s contract, which should help them stay away from the top of their farm system. Domínguez will help lengthen Seattle’s right-handed setup corps, with a 4.10 ERA and 45 strikeouts in 37 ⅓ innings this season. Jones has MLB experience with the Guardians and Rockies and has had a .752 OPS in 38 games for the White Sox’s Triple-A affiliate this season. The 23-year-old Smith is a legitimate prospect, boasting a .291/.448/.589 batting line with 22 home runs and 74 walks across three different minor-league levels.
The White Sox have received a solid pitcher in Castillo, who will slot in at or near the back of their rotation. However, they could have traded for a better pitcher, and Castillo is showing signs of decline.
The Mariners, on the other hand, have cleared a rotation logjam and shed Castillo’s contract, which will save them at least $15.95 million in total salary and potentially as much as $40.95 million. They will now have the financial flexibility to improve their roster, and this trade is just the beginning.
Grades for the Trade
Chicago White Sox: B
The White Sox have gotten their guy without giving up a top-line prospect, but they could have traded for a better pitcher. They have bolstered their rotation with Castillo, who will take the ball every fifth day like clockwork.
Seattle Mariners: A
The Mariners have saved a significant chunk of change and cleared a rotation logjam. They will now have the financial flexibility to improve their roster, and this trade is just the beginning.
The Mariners have received a legitimate prospect in Smith, who is an arrow-up prospect with a combination of power and selectivity. They will now have the opportunity to improve their roster and compete for a playoff spot.
