White Sox acquire righty Castillo from Mariners in 4-player trade

ST. PETERSBURG – As of 11 p.m. EST Saturday night, the White Sox stood as the lone team above .500 in the American League Central.

They also added strength to their hold on the division and their pitching staff by acquiring right-handed pitcher Luis Castillo from the Seattle Mariners for right-hander Seranthony Domínguez, Minor League catcher Boston Smith and Minor League outfielder Nolan Jones.

The White Sox are picking up the remainder of Castillo’s salary, which includes the portion of the $22.75 million owed in 2026 and the $22.75 million for '27, totaling roughly $30 million guaranteed.

Castillo, 33, has a $25 million vesting option for '28 if he pitches at least 180 innings in 2027. Through 20 games for the Mariners in 2026, of which 17 were starts, the veteran right-hander has a 3-9 record with a 5.06 ERA and 86 strikeouts over 99 2/3 innings. Those numbers are a stark contrast to his past success, when Castillo was a three-time All-Star and made the Midsummer Classic as recently as '23.

TRADE DETAILS
White Sox receive: RHP Luis Castillo
Mariners receive: RHP Seranthony Domínguez, OF Nolan Jones, C/OF Boston Smith (formerly Chicago's No. 15 prospect, now SEA No. 14)

In 13 of his last 17 starts, Castillo allowed four runs or fewer. He received three runs of support or less 15 times. Castillo last pitched on July 28 at Dodger Stadium, allowing five runs on 11 hits over five innings, with two strikeouts.

Since May 25, Castillo has a 3.88 ERA over 10 games. He would be in line to start the Tuesday opener in Boston.

Domínguez, 31, is 4-3 with a 3.99 ERA, a team-high 12 saves, four holds and 47 strikeouts over 38 1/3 innings over 43 relief appearances this season, his first with the White Sox. He was earning $7 million this season, $10 million in '27 and has a mutual option at $12 million for '28.

The White Sox made the astute move of using Domínguez in lower-leverage situations after he struggled in save situations. Over his last 10 games, covering 8 2/3 innings, Domínguez has allowed one earned run, struck out 11 and walked five.

The White Sox are clearly going for it in '26, while keeping an eye on the future. They don’t appear inclined to trade any of their top 10 prospects. Smith, 23, was Chicago's No. 15 prospect, while Jones was not in MLB Pipeline's top 30.

But they also have proven to be as strong as any team in the AL, with a 3-3 record against the Yankees and Rays over the past week, and know there’s more there for the team beyond the AL Central. Castillo has appeared in six career postseason games (five starts), producing a 2-3 record with a 2.25 ERA. He earned the victory in the deciding Game 5 of the 2025 ALDS vs. Detroit with 1 1/3 scoreless innings of relief.

White Sox pitching has been especially strong over their past 39 innings, yielding two earned runs on 22 hits. That stretch featured one run allowed over five innings from Erick Fedde in Friday’s 6-1 victory and Noah Schultz allowing one run in five bulk innings Saturday as part of a 1-0 loss. It will be interesting to see how the White Sox rotation will soon line up behind Sean Burke, who has emerged as a true No. 1 after posting a 1.14 ERA in July, and Davis Martin, with general manager Chris Getz figuring to be active before the Trade Deadline at 5 p.m. CT Monday.