Luis Castillo Trade Grades: White Sox Get Much-Needed Veteran Starter

The White Sox, sitting atop of the AL Central, made a big move Saturday night.

Castillo is a three-time All-Star with a career 3.65 ERA over 10 years in the big leagues. | IMAGN IMAGES via Reuters Connect

With two months left in the regular season, the White Sox sit in first place in the AL Central. And on Saturday night, they let the rest of the division know they’d like to keep it that way. 

ESPN’s Jeff Passan reported Saturday night that Chicago acquired right-handed pitcher Luis Castillo in exchange for reliever Seranthony Dominguez, outfielder Nolan Jones and catching prospect Boston Smith.

The South Siders are buyers at the trade deadline. The Mariners are trying to thread the needle, offloading a starting pitcher they don’t really need anymore to add a bullpen arm and a bat that could help them in the future.

Let’s get out the red pen and grade the deal for both teams.

Chicago White Sox

In his last outing in a Mariners uniform, Castillo allowed five runs in five innings in Seattle’s 7–6 win over the Dodgers on July 28. | IMAGN IMAGES via Reuters Connect

It’s been a great summer for the South Siders.

After back-to-back last-place finishes in the AL Central, the White Sox (58–52) enter Sunday’s slate of games with a 2 ½ game cushion in first place. They have rode their homer-happy offense to the top of the standings with Collin Montgomery (25 homers), Munetaka Murakami (24) and Miguel Vargas (23) leading the charge. 

The White Sox’ starting rotation needed work. It’s been a middle-of-the-pack unit thus far with a 4.28 ERA, and it ranks 26th in strikeouts. To boost their rotation, White Sox general manager Chris Getz swung big for Castillo, a three-time All-Star in the middle of a down year. 

Castillo has been one of the most consistent pitchers in baseball over the last decade. In 2025, he logged an 11–8 record, 3.54 ERA and 18 quality starts for the Mariners. But those numbers have plummeted this season, as Castillo enters the month of August with a 5.06 ERA and -0.7 bWAR in 20 appearances (17 starts). He has surrendered four or more earned runs in seven of those outings with just three quality starts. 

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Castillo’s fastball uncharacteristically has been knocked around this year. Opponents are batting .251 against the pitch with a .473 slugging percentage—compared to just .203 and .411 last year, respectively. And his strikeout rate has steadily declined from 27.3% in 2023 to a below-average 19.4% this year.

It’s a big financial risk. Castillo, 33, is owed $24.2 million next year and has a $25 million vesting option in 2028 if he reaches 180 innings next year. According to ESPN, the White Sox are absorbing all of the remaining money on his deal, including the prorated slice of his $24.2 million salary this year.

Still, Castillo is a big upgrade for the pitching-needy White Sox this year. Adding a veteran presence who will slide into their playoff rotation—and not giving up much for it—is a win for Chicago. That being said, if Castillo is the only starting pitcher the Sox are going to add, don’t count on them making noise in October if they get there.

Grade: B

Seattle Mariners

Seranthony Domínguez logged 12 saves and a 4.10 ERA for the White Sox this season. | IMAGN IMAGES via Reuters Connect

Seattle is moving on from one of the key cogs in its rotation since Jerry Dipoto acquired him from the Reds at the 2022 trade deadline.

For the Mariners, the move makes sense. Seattle frees up plenty of cash for next year and beyond on a pitcher who is showing signs of slowing down at 33. They might have gotten out of the Castillo business at the right time.

The Mariners get back veteran reliever Seranthony Dominguez, a 31-year-old journeyman reliever who picked up 12 saves for the White Sox this season but has a 4.10 ERA and even worse underlying metrics, as his control appears to have abandoned him the last two years. He’s dished out 59 free passes in 100 innings over that span. Seattle won’t be happy about paying him $10.5 million next season, but they still come out ahead financially in this deal.

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Nolan Jones, who once looked like a promising piece in Colorado after finishing fourth in NL Rookie of the Year voting in 2023, hasn’t sniffed the big leagues this year and logged a .618 OPS over 215 games in ’24 and ’25 combined. 

Boston Smith, a 2025 sixth-round pick by the Nationals whom the White Sox traded for in March, has worked his way up to Double A this season and is batting .291/.448/.589 in the first 78 games of his professional career. He may not stick behind the plate as his defense needs work, but Smith has the athleticism to play almost anywhere on the diamond and his performance at the plate this year is beyond what could have been hoped for.

Considering the exciting pitching talent coming up the Mariners’ system in Kade Anderson (ranked as SI’s No. 15 prospect in baseball) and Ryan Sloan (No. 25), shedding themselves of Castillo’s deal in a lost season was a smart move—even though they probably didn’t get much in return.

Grade: B+

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