The Chicago White Sox have acquired veteran right-handed starting pitcher Luis Castillo from the Seattle Mariners in exchange for right-handed reliever Seranthony Domínguez, outfielder Nolan Jones and catcher prospect Boston Smith, the teams announced late Saturday.
Castillo, 33, hasn't been up to his usual standards this season. Beyond the top-line struggles, his current FIP of 4.57 is a career-worst mark. That said, the overall body of work is strong -- he has a career ERA+ of 115 and three All-Star selections across parts of 10 MLB seasons -- and in 2025, he had a 108 ERA+ and a sub-4.00 FIP in 32 starts. Castillo has topped 30 starts in each of the last three seasons. Castillo figures to slot in at or near the back of the Chicago rotation, with Davis Martin, Sean Burke, and Erick Fedde slotting in at the front and middle.
Castillo is under contract through the 2027 season with a vesting option for 2028 in his contract:
Source: The White Sox will absorb all of the remaining money on Luis Castillo's contract in the trade. So, the pro-rated portion of $22.75M this year and $22.75M next year. Castillo's deal also has a $25M vesting option for 2028 if he reaches 180 innings.
— Alden González (@Alden_Gonzalez) August 2, 2026
The White Sox had been seeking to bolster their rotation ahead of Monday's trade deadline as they attempt to maintain their lead in the American League Central. As for the Mariners, they remain in contention in the weak AL West, and they have been expected for some time to deal from their rotation depth in order to address roster needs elsewhere.
On that front, Domínguez, 31, will help lengthen Seattle's right-handed setup corps. This season with the White Sox, he's pitched to a 4.10 ERA with 45 strikeouts and 21 unintentional walks in 37 ⅓ innings. He also has 12 saves this season. Jones, 28, has MLB experience with the Guardians and Rockies, and this season he's had a .752 OPS in 38 games for the White Sox's Triple-A affiliate. The 23-year-old Smith is a former sixth-rounder out of Wright State. In this, his first professional season, he's batted .291/.448/.589 with 22 home runs and 74 walks across three different minor-league levels. He's spent the last 22 games at the Double-A level.
Here now are our grades for this 3-for-1 swap between American League postseason hopefuls.
Chicago White Sox: B
White Sox get their guy without giving up a top-line prospect
Even after Saturday's loss, the upstart White Sox are atop the AL Central with a three-game lead in the loss column. Rotation help, particularly a non-rental they could keep next season, headlined the deadline shopping list. Sean Burke and Davis Martin have been very good, collectively. Erick Fedde, Anthony Kay, and rookie Noah Schultz have been more hit-and-miss.
This is at least a little bit concerning:
- April and May: 3.92 ERA and .704 OPS allowed
- June and July: 4.75 ERA and .759 OPS allowed
Chicago's rotation has been trending down, whereas Castillo is trending up. Eight starts into the season, he was sitting at a 6.57 ERA. It's a 4.11 ERA since, which isn't amazing, but the guy takes the ball every fifth day like clockwork, and there's value in that reliability. Castillo has allowed no more than two earned runs in six of his last 10 appearances.
The White Sox absorbed the entirety of Castillo's contract, allowing them to stay away from the top of their farm system. Domínguez never really fit into the bullpen mix, and sending his contract to Seattle softens the financial blow. Jones is a spare part outfielder who was unlikely to see meaningful time on the South Side. Smith is a legitimate prospect and the cost of doing business.
For all intents and purposes, the White Sox brought in a veteran innings guy at minimal prospect cost and fairly significant financial cost, but it's just money. They'll live. I can't go up to an A because Castillo is showing some signs of decline and I would have rather seen the White Sox trade legitimate prospects for a better pitcher, but this deal works too. Solid work.
Seattle Mariners: A
Mariners save a chunk of change -- now what do they do with it?
This A is predicated on the assumption that the Mariners will now not trade George Kirby or Emerson Hancock, which had been rumored in recent days. Trading a starter made sense. Seattle had six good starters for five rotation spots, which led to some clunky schedules and piggyback situations. Castillo was the guy to move, given his age and salary, and they moved him.
For the Mariners, the trade boils down to Castillo for Smith and salary relief. Jones, the former Rockie, is a fourth outfielder type having a good but not amazing season in Triple-A. Domínguez is an enigmatic medium-ish-leverage reliever who looks like a world-beater one day and un-pitchable the next. Nevertheless, he'll aid Seattle's middle relief unit.
Financially, the Mariners are saving a pretty nice chunk of change between this year and next. Here's the salary breakdown:
| Castillo | Domínguez | Savings | |
|---|---|---|---|
Rest of 2026 | $7.5M | $2.3M | $5.2M |
2027 | $22.75M | $10M | $12.75M |
2028 | $25M vesting option | $12M mutual option ($2M buyout) | ? |
Castillo's 2028 option vests with 180 innings in 2027 and a clean bill of health after that season. The Mariners will pay Domínguez a $2 million buyout in 2028 (mutual options are always declined by one side or the other) and not have to worry about being on the hook for Castillo's age-35 season. They've saved at least $15.95 million in total salary and potentially as much as $40.95 million.
Of course, what the Mariners do with the savings remains to be seen. Ownership could pocket it, which would be shameful, or could put it back into the roster. It's impossible to say, especially with a new collective bargaining agreement on the horizon. We have no idea what the sport's economics will look like next year. We do know, though, that the Mariners saved a ton of cash.
Smith, 23, came over from the Nationals in the Curtis Mead trade in March. He's hitting .291/.448/.589 and has reached Double-A this season. MLB Pipeline ranked him as Chicago's No. 15 prospect before the trade and praised his "combination of power and selectivity." His defense is rough around the edges, but Smith is an arrow-up prospect. Now he's a Mariner.
Clearing the rotation logjam and shedding Castillo's contract is good work, assuming the Mariners now take steps to improve the roster. Dominguez will help the middle relief situation and Smith could be a player down the road. I'm giving the Mariners an A based on the assumption that they use the newfound financial flexibility to improve the team, and this isn't their big deadline move.
