The biggest move before the Aug. 3 MLB trade deadline landed with a jolt: the Seattle Mariners and Chicago White Sox struck a rare deal between two contending teams, with Seattle sending three-time All-Star Luis Castillo to Chicago.
The White Sox, who are leading the American League Central, are getting the veteran right-hander in exchange for reliever Seranthony Dominguez, outfielder Nolan Jones and catching prospect Boston Smith, according to multiple reports. ESPN’s Jeff Passan first reported the trade was in place.
For the Mariners, the move clears up the cloud hanging over a six-man rotation that had been a season-long talking point. Seattle had been carrying Bryce Miller, George Kirby, Emerson Hancock, Bryan Woo, Logan Gilbert and Castillo, even as the club tries to steady itself after its first-ever run to the AL Championship Series a year ago. Castillo, 33, had become the odd man out in that group, and also the oldest arm in a rotation otherwise built around pitchers 28 or younger when the season began.
Chicago is taking on the full contract, including the prorated portion of Castillo’s $22.75 million salary this year and the same figure next year, according to ESPN’s Alden Gonzalez. The deal also includes a $25 million vesting option for 2028 if Castillo reaches 180 innings in 2027.
There’s risk on both sides here, and neither club is buying low on a player who has been cruising. Castillo is three years removed from his last All-Star nod and arrives with a 3-9 record and a 5.06 ERA across 20 appearances, 17 of them starts. His walk rate and strikeout rate, once major strengths, have both moved in the wrong direction.
Dominguez comes to Seattle with his own questions. The 31-year-old signed a two-year, $20 million deal with the White Sox in January, but the results have been uneven. He has 12 saves and has struck out 28 percent of opposing hitters, yet he has also blown five save chances and allowed home runs at twice the rate he did in 2024, when he split time between the Baltimore Orioles and Toronto Blue Jays.
Seattle won’t need Dominguez to handle the ninth inning, because Andres Muñoz already has that job locked down. Dominguez should fit into a setup role, while Jones, who has spent the entire season at Triple-A, is expected to go to the minors.
The most interesting piece for the Mariners may be Smith. MLB Pipeline lists the 23-year-old catcher as the No. 15 prospect in the White Sox system, and he had been stuck behind Kyle Teel and Edgar Quero on the organizational depth chart.
At Double-A Birmingham, Smith hit .306/.479/.667 in 22 games. He won’t impact Seattle this season, but he’s the kind of prospect a team is willing to move only when it believes the return justifies it. The one wrinkle here is that he’s heading to a team still in the postseason race, and in the same league as Chicago.
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Mariners Face A Deadline Decision Fans May Not Like
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The complication is the cost. San Diego is believed to be asking for pitching prospect Kade Anderson, and that puts Seattle in a familiar spot for a contender trying to balance the present against the future. Anderson is viewed as close to the majors and could be in line for his debut this year, so the Mariners have to decide whether immediate relief help is worth parting with a pitcher they may not have to wait much longer to see. [Read more 🡒]