One of the biggest needs for the Chicago White Sox was starting pitching. They have seemingly gotten that with a deal with the Seattle Mariners on Saturday night. The White Sox acquired Luis Castillo in exchange for Seranthony Domínguez, Nolan Jones, and Boston Smith. This is a type of deal that, on the surface, is a win for both sides. Both teams were able to address an area of need that will hopefully make them better for the final push. But is this enough to fix the problem they have?
Why both teams decided to make the Castillo trade
The White Sox Perspective
While Castillo is a well-known pitcher, he has not seen much success in 2026. In 99 2/3 innings, he has a career-worst 5.09 ERA with 86 strikeouts to 32 walks, a 1.395 WHIP, and an ERA+ of 78. He even lost a rotation spot and was used in a piggyback role. But the Sox are buying him for his track record. Over his 10 seasons in the show, he has an ERA of 3.65 and an ERA+ of 115. He is also under contract until 2027 with a vesting option for 2028. This is not just a move for this year but the foreseeable future. In an ideal world, Castillo can be a top-of-the-rotation starter for the foreseeable future.
The White Sox just need to figure out what has caused him to struggle as of late. The two biggest areas they need to address are the quality of contact and his strikeout numbers. This season, he has allowed a 41.7 HardHit% and a 35.5 Launch Angle Sweet Spot%. This has become a trend for Castillo, as last season he ranked in the bottom eight percentile of HardHit%. Giving up this quality of contact is a big reason why his ERA continues to increase year after year. His strikeout percentage has also dropped to a career-worst 19.4%. Earlier in his career, it sat around 25%. It’s a risky move, but it can pay off if the White Sox can straighten him out.
The Mariners Perspective
While it’s strange to see the Mariners sell when they are only two games out of a playoff spot, they are dealing from a position of strength. The Mariners have one of the best starting rotations in baseball. Even after trading Castillo, they still have five starters who can dominate on any given night. Trading from a position of strength to upgrade other areas is a very savvy move by their front office. The big get is Dominguez. The back end of the Mariners bullpen has been a major question mark. Dominguez doesn’t fix it, but at the very least improves it. In 38 1/3 innings, he has a 3.99 ERA with 47 strikeouts to 23 walks, a 1.330 WHIP, and an ERA+ of 107.
The other big acquisition is Smith. He was the 15th overall prospect in the White Sox system; now he is the 14th in the Mariners system according to MLB Pipeline. He has been praised for his selectivity and ability to hit for power. His ability to pull the ball to right field has allowed him to increase his power numbers. He is also one of the more athletic catchers in the minors. He has solid speed that makes him a threat on the base paths. A very rare ability to have as a catcher. Jones is nothing more than a depth piece. He has been solid in Triple-A this season, but should be nothing more than a fourth outfielder.
