Mariners trade Luis Castillo to White Sox for three players

Mariners trade Luis Castillo to White Sox for three players

The Seattle Mariners have traded right-handed starting pitcher Luis Castillo to the Chicago White Sox in exchange for right-handed relief pitcher Seranthony Domínguez, outfielder Nolan Jones, catching prospect Boston Smith, and cash considerations, the team announced Saturday night.

The move comes as the struggling Mariners sit four games below .500 and trail the Houston Astros by three games in the AL West. The Chicago White Sox, currently leading the AL Central by 2 1/2 games with a 58-52 record, acquire a three-time All-Star as they attempt a playoff push.

Castillo, 33, has struggled during the 2026 campaign, posting a 3-9 record with 86 strikeouts and a 5.06 ERA over 99 2/3 innings. His performance led to a brief demotion from the Seattle rotation. However, the White Sox may be betting on a return to form; Castillo has maintained an ERA under 4.00 in eight of his previous nine seasons and finished 2024 with a 3.64 ERA in 175.1 innings.

The trade also provides significant financial relief for Seattle. By moving Castillo, the Mariners shed approximately $30 million in salary for the remainder of this season and 2027. Castillo is under contract through 2027, earning $24.2 million in each of the next three years. His contract includes a $25 million vesting option for 2028 if he pitches at least 180 innings in 2027.

Analyzing the Return

Seattle receives a mix of established major league experience and youth in the return:

• Seranthony Domínguez: The 31-year-old right-hander is 4-3 with a 4.10 ERA in 42 games this season.
• Nolan Jones: The 28-year-old outfielder has not appeared in a major league game for Chicago this year, instead splitting time between Triple-A Charlotte and Triple-A Columbus.
• Boston Smith: The 23-year-old catching prospect is hitting .291 with 22 home runs and 58 RBIs across three minor league levels. Smith was originally selected by the Washington Nationals in the sixth round of the 2025 MLB draft before being traded to Chicago in March for utility man Curtis Mead.

Roster Implications and Depth

The Mariners' decision to part with one of their longest-tenured players follows a difficult trajectory. After reaching the ALCS for the first time in 24 years last season, the team experienced a step back this year, hampered in part by injuries to Cal Raleigh, who failed to repeat an MVP-caliber performance. Additionally, the front office faced constraints during an "extremely quiet" offseason when ownership provided roughly $15 million to $20 million for roster additions, resulting in only one free agent signing: Donovan Solano.

Despite the loss of Castillo, Seattle maintains a deep starting rotation. Manager Dan Wilson previously utilized a "piggyback" system pairing Castillo with Bryce Miller to ensure all six starters appeared regularly. The rotation still includes Miller, George Kirby, former first-round pick Emerson Hancock, and former All-Stars Logan Gilbert and Bryan Woo. The team also has left-handed prospect Kade Anderson at the Double-A level.

The departure of Castillo may signal further changes in Seattle. While the Mariners indicated for most of July that they would not trade George Kirby, a person briefed on discussions noted that the team is now open to moving him. Kirby is under club control through 2028, meaning the Mariners would require a substantial offer, potentially involving young pitching, to finalize such a deal.

For the White Sox, Castillo represents a durable addition to the rotation. He has started at least 30 games in each of the past three seasons and has 228 starts since 2018, ranking third in MLB. Over 10 seasons and 263 career games, he holds an 87-93 record with a 3.65 ERA and 1,579 strikeouts.

The trade was finalized ahead of the league's trade deadline on Monday.