On Saturday evening, Jeff Passan broke the news that the White Sox (58-52) have acquired starting pitcher Luis Castillo from the Mariners (54-58). In exchange, Seattle received reliever Seranthony Dominguez, Triple-A outfielder Nolan Jones, and Double-A catcher Boston Smith.
Castillo, 33, is set to join the starting rotation on the South Side. In 2026, Castillo has posted a 5.06 ERA and a 4.57 FIP in 99 2/3 innings. It has been a down year for Castillo, who has only accumulated 0.6 fWAR this season.
Overall, Castillo has put together an impressive career, posting a 3.65 ERA, a 3.78 FIP, and 27.0 fWAR across 10 seasons. Castillo is a three-time All-Star who finished fifth in the American League Cy Young race in 2023.
Castillo’s numbers have declined significantly since last year (3.54 ERA, 3.88 FIP, 2.6 fWAR in 180 2/3 innings). This decline is noticeable, and the White Sox are aware that they are not acquiring the type of player that Castillo previously was. Castillo’s fastball still has plenty of legs (95.3 mph on average, 64th percentile, slightly up from 2025). However, the effectiveness of his breaking balls has declined sharply. Castillo’s primary breaking ball and his second-most common pitch is his slider, which held opposing hitters to a measly .271 wOBA in 2025. By contrast, in 2026, batters have a .352 wOBA against it, a sizable increase. Repairing that slider is probably task No. 1 with regard to getting Castillo closer to his 2017-2025 self.
Castillo is being paid $24.15 million in 2026, and he is under team control through 2027, when he will earn the same salary. Most likely, Castillo will become a free agent at the end of the 2027 season. If Castillo pitches 180 innings in 2027, an option for 2028 will vest, and he will earn $25 million, but the White Sox would likely avoid that.
Domínguez, 31, is the only active major leaguer going to the Mariners in this trade. Domínguez has posted a 3.99 ERA and a 4.64 FIP in 38 1/3 innings as a reliever on the South Side this year. Prior to this season, the White Sox signed him to a two-year, $20 million contract. Entering the season, Domínguez was expected to be a high-leverage reliever, but he has not quite lived up to the hype.
Jones, 28, has posted a .247/.336/.396 (95 wRC+) slash line with 2.7 fWAR across four MLB seasons. Jones has played all of 2026 in Triple-A, where his slash line has been .257/.362/.445 (107 wRC+). Jones was quite good in 2023, when he accumulated an impressive total of 3.8 fWAR, but besides that, he has not accomplished much worth speaking of at the MLB level.
Smith, 23, is a potentially spicy prospect who has been tearing it up this season. On paper, Smith is the hardest piece to lose among the players leaving the White Sox organization. Across 78 games (eight with Single-A Kannapolis, 48 with High-A Winston-Salem, and 22 with Double-A Birmingham), Smith has slashed .291/.448/.589, as pitchers have not had many answers for him. The White Sox have had trouble at the catcher position all season, and Smith is a catcher who has been raking left and right. Prior to the trade, Smith had earned the No. 15 spot on MLB Pipeline’s White Sox prospect rankings. The White Sox traded Curtis Mead for Smith in March, and Smith was hardly on anyone’s radar at that point. However, given his timeline, he was very unlikely to contribute in the majors this season.
Ultimately, Domínguez did not lock down a primary setup or closer role in the White Sox bullpen, and Jones is not looking like a long-term solution in the majors. As a result, this trade boils down to an exchange of a potentially spicy prospect for a veteran pitcher slightly past his prime who carries a sizable contract through 2027. If Castillo’s numbers get closer to how they were from 2017-2025, this trade will be perfectly fine. The key issue is whether Castillo still has enough baseball left to be a significant piece of a playoff contender.
