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Trade details: Chicago White Sox acquire right-hander Luis Castillo from the Seattle Mariners for right-hander Seranthony Domínguez, catcher/outfielder Boston Smith, and outfielder Nolan Jones
I’ve been writing for a little while that the Mariners needed to kick Luis Castillo to the curb with Kade Anderson marching through Double A like an angrier General Sherman, but the $30 million left on Castillo’s contract — while a sunk cost for Seattle — through the end of 2027 was going to be an impediment to any deal. They found a partner in the feel-good hit of the summer, the White Sox, and even got a real prospect in return along with a platoon outfielder who might help the Mariners right away.
Catcher/outfielder Boston Smith was the Nationals’ sixth-round pick last year out of Wright State, where he’d hit .330/.498/.770 with 26 homers, but was a 22-year-old senior in the very mediocre Horizon League. The new front office in Washington traded him before he played his first professional game, sending him to Chicago for Curtis Mead, a deal that worked out for both teams, as Smith has taken off in pro ball. He started in Low A, quickly moved to High A and raked, with the major caveat that 23 is quite old for that level. The Sox promoted him to Double A on July 1 and he’s hit .306/.485/.667 in 23 games, with a 27.8 percent strikeout rate so far, at a level that’s at least appropriate for his age and experience.
In the least surprising development ever, Smith has run into trouble at Double A with offspeed stuff, likely far better than anything he ever saw in college or saw more than once or twice a week in high A. He’s missed 42 percent of the time he’s swung at anything that wasn’t a fastball at the new level, in a sample small enough to hope he can bring it down with time and more looks, but also a potential reason to argue the White Sox sold high on him.
Smith has played all over the place between college and his one year in the minors, getting reps everywhere but first and on the mound, but the real appeal here is that he might be able to catch. He’s very athletic and moves well but has less than 500 innings behind the plate since high school, so he’ll need a good bit of work across the board, including firming up his throwing. He’s an above-average runner so if he has to move out from behind the plate he should offer defensive value somewhere in the outfield.
There’s a very wide range of potential outcomes for Smith: He could end up struggling to hit quality offspeed stuff to the point that he isn’t a viable big leaguer, he could end up a fringy defensive catcher with enough power to be someone’s regular, or anything in between. (Since I get this question a lot on prospects who’ve broken out like he has, he’s not a top 100 prospect, and probably not in the Mariners’ top 10.)
Nolan Jones is a platoon right fielder who had a fluke year for the Rockies in 2023 but hasn’t hit at all in the majors since then; he’s spent the year in Triple A, first with Columbus (Cleveland) then with Charlotte (White Sox), hitting .281/.394/.482 off right-handed pitching. Seattle has been playing Bobby Bupkis in right field most of the season, and while that’s not their worst position for offense, it’s probably the easiest one for them to address, and Jones might actually be useful for them. The Mariners also added veteran right-handed reliever Seranthony Dominguez, who’s effective against right-handed batters but shouldn’t face many lefties, to add to their middle relief corps.
As for Castillo, the Mariners needed to shed any of his salary that they could, and also benefit from getting him off the roster, since he was actively hurting the team with his performance. Hitters have been hitting his whole arsenal hard this year, with his four-seamer going from consistently plus (worth +11 to +21 runs saved per year from 2022-25) to a batting-practice pitch (-5 runs “saved” this year, with hitters slugging .473 off it). His slider, never great, has backed up slightly, and it’s gotten hammered too; only his changeup has stayed steady in shape and results, and it wasn’t a good pitch in 2025, either. He’s a low-slot guy who doesn’t spin the ball well and doesn’t have a great changeup to keep hitters off the fastball. He only has to be better than Noah Schultz has been to help Chicago this year, and perhaps the White Sox may see something they can adjust to get him above replacement level for 2027.
