White Sox trade with Mariners to add rotation splash, ditch Seranthony Dominguez problem

After weeks of speculation and rumors, the Chicago White Sox have made their first of likely several deadline trades. According to multiple reports, the team has acquired RHP Luis Castillo from the Seattle Mariners in exchange for reliever Seranthony Dominguez, minor league outfielder Nolan Jones, and catching prospect Boston Smith. The White Sox will absorb the entirety of Castillo’s contract, which will pay him a prorated portion of $22.75 million this season and $22.75 million next year. He also has a $25 million option for 2028 that vests if he reaches 180 innings pitched in 2027. 

Castillo, 33, isn’t having the type of year fans are used to seeing from him. The starter has a 5.06 ERA in 20 outings, totaling 99.2 innings after posting a sub-4 ERA in each year since 2019. The Mariners have had a surplus in their starting rotation and have been rotating their starters between the rotation and the bullpen, which Castillo has vocally criticized this season. A change of scenery could be just what he needed to get back on track. At his best, Castillo has frontline upside and has performed well in the playoffs, posting a 2.25 ERA in six postseason outings. He’s reached at least 175 innings pitched in each of the past three seasons and should give the White Sox a high-upside arm that can pitch deep into games. The White Sox can safely pencil him into their rotation for 2027 as well. 

The White Sox surrendered an interesting return to stabilize their rotation

The return for Seattle is an intriguing aspect of this trade. For starters, the Mariners will receive RHP Seranthony Dominguez, who the White Sox signed to a two-year, $20 million deal this offseason. Dominguez struggled in the closer role and was ultimately removed, and has performed slightly better in lower leverage spots. The White Sox have a few pitching prospects they’re considering promoting to the bullpen and have been in the hunt for relievers as the deadline approaches, so getting someone to take Dominguez is a savvy move by the front office. His salary will help offset the hefty amount the White Sox owe Castillo over the next two seasons. 

Nolan Jones had a great season with the Rockies in 2023 but his numbers have dipped in the days since. He’s hitting .255 with an .804 OPS in 91 games between the White Sox and Guardians Triple-A affiliates and has not played in the big leagues in 2026. 

The main piece here is Boston Smith. The White Sox added Smith in the Curtis Mead trade at the beginning of the season and all he’s done is hit since. Smith is hitting .291 with a 1.037 OPS and 22 home runs between three minor league affiliates. He’s spent time at catcher and in the outfield this season so there’s a bit of uncertainty about his long-term position. Still, his bat should play as he reaches the higher levels of the minor leagues. 

I don’t believe Luis Castillo should be the only trade the White Sox make this weekend. They could still use another reliable starter and they need a catcher, but it’s a more exciting option than they could’ve chosen to go with. Castillo has years of track record being a top-of-the-rotation arm, and the White Sox clearly believe they can unlock more than he’s done this season. 

I think it was a gamble worth taking for the White Sox, and it makes them a better team for 2026 and beyond.

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