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

ST. PETERSBURG -- Chris Getz fueled the White Sox playoff push with the addition of right-hander Luis Castillo via a trade with Seattle, as announced on Saturday night.

And the general manager presiding over the American League’s No. 2 seed and the only team over .500 in the AL Central entering Sunday might not be finished, with Monday’s Trade Deadline approaching at 5 p.m. CT.

“This was an opportunity to bring in a starting pitcher that we're really excited about,” Getz said during a Sunday morning Zoom call. “Someone that can help lead this young pitching staff. Not only cover innings, but has experienced pitching in the playoffs.

“We're at the bottom of the league in regards to starting pitching innings. And so to be able to insert someone that pitches as regularly, posts as often as Luis Castillo, has the credibility into this group, we felt like it is going to make a meaningful step in the right direction.”

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)

Castillo, who will join the team in Boston and make his Chicago debut in Thursday's series finale at Fenway Park, was acquired in exchange 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, adding up to roughly $30 million guaranteed.

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

In 13 of his last 17 starts, Castillo has allowed four runs or less. He has received three runs or less of support 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. Castillo moves into the rotation, while Erick Fedde transfers to the bullpen but will stay stretched out.

“We talked to Luis Castillo last night, and gosh, he was so excited. He was. He's just ready to get going,” Getz said. “You could hear it in his voice. And I said, ‘Listen, I can't wait to meet you in Boston.’ I know [manager] Will [Venable] and the players and the staff, they feel the same way.”

Domínguez 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. The 31-year-old was earning $7 million this season, $10 million in ‘27 and has a mutual option at $12 million for ‘28 with a $2 million buyout.

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

This White Sox team clearly is going for it in ‘26, while keeping an eye on the future. They don’t appear inclined to trade any of their Top 100 prospects, at least not for rentals, as Getz explained on Sunday.

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 this 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 ⅓ scoreless innings of relief.

Adding a catcher rates as another move Getz expects to execute before Monday night, with starter Kyle Teel sidelined by a left high ankle sprain keeping him out six to 12 weeks. Another pitcher, be it a starter or reliever, could stoke this team’s fire even higher than it currently stands.

“If we feel like it can really help this club and it comes at a reasonable prospect cost, we’ll look at it,” Getz said. “I am sensitive to the clubhouse and this group and what they are accomplishing right now and not being disruptive to this group.

“They have done something really special so far this season. They believe they can win on a nightly basis and they are proving that. Trying to find ways to really fuel this club without disrupting the chemistry clearly exists within that clubhouse.”