Luis Castillo traded to White Sox: Mariners starter to bolster Chicago rotation hanging on to division lead

The Chicago White Sox have acquired veteran right-handed starting pitcher Luis Castillo from the Seattle Mariners in exchange for right-handed reliever Seranthony DominguezDomínguez, outfielder Nolan Jones and catcher prospect Boston Smith, ESPN reports. 

Castillo, 33, hasn't been up his usual standards this season. Beyond the top-line struggles, his current FIP of 4.57 is a career-worst mark. That said, the overall body of work is strong -- he has a career ERA+ of 115 and three All-Star selections across parts of 10 MLB seasons -- and 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. Castillo figures to slot in at or near the back of the Chicago rotation, with Davis Martin, Sean Burke, and Erick Fedde slotting in at the front and middle. 

Castillo is under contract through the 2027 season with a vesting option for 2028 in his contract: 

Source: The White Sox will absorb all of the remaining money on Luis Castillo's contract in the trade. So, the pro-rated portion of $22.75M this year and $22.75M next year. Castillo's deal also has a $25M vesting option for 2028 if he reaches 180 innings.

— Alden González (@Alden_Gonzalez) August 2, 2026

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. As for the Mariners, they remain in contention in the weak AL West, and they have been expected for some time to deal from their rotation depth in order to address roster needs elsewhere. 

On that front, Domínguez, 31, will help lengthen Seattle's right-handed setup corps. This season with the White Sox, he's pitched to a 4.10 ERA with 45 strikeouts and 21 unintentional walks in 37 ⅓ innings. He also has 12 saves this season. Jones, 28, has MLB experience with the Guardians and Rockies, and this season he's had a .752 OPS in 38 games for the White Sox's Triple-A affiliate. The 23-year-old Smith is a former sixth-rounder out of Wright State. In this, his first professional season, he's batted .291/.448/.589 with 22 home runs and 74 walks across three different minor-league levels. He's spent the last 22 games at the Double-A level.