Two days before the Aug. 3 MLB trade deadline, the Seattle Mariners and Chicago White Sox completed what is widely viewed as the biggest blockbuster deal of the 2026 season.
According to multiple reports, Chicago acquired three-time All-Star starting pitcher Luis Castillo from Seattle.
In return, the Mariners received reliever Seranthony Dominguez, outfielder Nolan Jones, and catching prospect Boston Smith. ESPN insider Jeff Passan was the first to report that the trade had been finalized.
The deal is notable because it involves two teams in the playoff race. The White Sox currently sit atop the American League Central, while the Mariners are just 2.5 games behind the final AL Wild Card spot.
For Seattle, the move addresses the ongoing challenge of managing its talented six-man rotation. Castillo, 33, had become the veteran of a staff headlined by Bryce Miller, George Kirby, Emerson Hancock, Bryan Woo, and Logan Gilbert.
While the younger pitchers emerged as the club’s core, Castillo became the most expendable member of the rotation.
ESPN’s Alden Gonzalez reported that the White Sox are taking on the remainder of Castillo’s contract, which could keep him in Chicago through the 2028 season if he reaches 180 innings pitched in 2027.
The trade carries risk for both organizations. Castillo has not returned to All-Star form since 2023 and owns a 3-9 record with a 5.06 ERA across 20 appearances (17 starts) this season, while his strikeout and walk numbers have both moved in the wrong direction.
Dominguez has also endured an inconsistent season after signing a two-year, $20 million contract with Chicago in January.
Although he has recorded 12 saves and maintained a strong strikeout rate, he has blown five save chances and surrendered home runs at a much higher rate than he did during the 2024 season with the Orioles and Blue Jays.
