Luis Castillo’s tenure as a Seattle Mariner has apparently come to an end. The Mariners announced tonight they have traded Castillo to the White Sox in exchange for reliever Seranthony Dominguez, outfielder Nolan Jones, and catching prospect Boston Smith. Per Daniel Kramer, the Mariners aren’t sending any money to offset the remainder of what Castillo is owed on the extension he signed in 2022, which runs through 2027 with a vesting option for 2028 if he reaches 180 innings.
In exchange, the Mariners
will be absorbing Dominguez’s not-insignificant salary for the remainder of this year and the next year of his contract, when he’s slated to make $10.5M. Dominguez also has an option for 2028, but it’s a mutual option (with a $2M buyout).
The 31-year-old Dominguez is on pace for the worst season of his career; he still collects strikeouts but his walk rate has ballooned over the past two seasons; he’s currently walking over 14% of batters faced. Compounding that problem is a serious case of dingeritis – a career-high 16.7% of fly balls he’s allowed have gone for homers, even in Chicago’s spacious confines. But he does still strike a lot of batters out and generate whiffs, he can still rush the fastball up at 97+, and he’s got a full complement of pitches for the Mariners pitching coaches to work with, even if he’s primarily a heater-sweeper pitcher as a reliever. It’s an expensive gamble, but the Mariners are both solving their rotation logjam (temporarily) and shedding Castillo’s contract in the move; if Dominguez can be Mariner-pitching-hive-minded into even a serviceable mid-innings arm, that’s a boon to the beleaguered bullpen.
The other pieces coming over in the trade are interesting in their own right. Nolan Jones is probably a name you’re familiar with if you were big into prospects a decade-ish ago; he was a second-rounder drafted by Cleveland in 2016 as a highly athletic two-sport athlete and attracted a lot of prospect attention as he made his way up the ladder for his 6’4” frame, easy raw power from the left side, and a star turn in the Arizona Fall League and the Futures Game in 2019. Unfortunately, injuries derailed his ascent, and he was dealt to the Rockies in 2023 for Juan Brito shortly after making his big-league debut. Now 28, Jones has spent time in the bigs but never really latched on consistently (outside of one 2023 season where he seemed to put it all together for Colorado), mostly due to a monstrous K rate compounded by the length of his swing. He’s been with the White Sox Triple-A team this season, blocked by the surprisingly good play at the big-league level, and will likely serve a similar role for Seattle as outfield depth at Tacoma.
Boston Smith is the third piece of the trade, and maybe the most interesting one, as he’s currently ranked as Chicago’s #15 prospect. To save you all time even though it’s lazy: the blueprint here is lefty-hitting Harry Ford, Take Two, with a power upgrade. A year after going undrafted, Smith was originally drafted by the Nationals in the sixth round in 2025 as a senior sign after a stellar year at Wright State that saw him tie for the lead in home runs in all of Division 1 baseball (26). The 5’10” Smith is listed as a C/OF, but despite being a plus athlete, as a catcher his skills are fringy enough he might not stick behind the dish, so he’s seen time in the outfield corners as well. Smith is selective at the plate, almost too much so – see, the Harry Ford comparisons weren’t that lazy after all – with a hilarious walk rate over 20%, but he’s been impressive in his first pro year, rocketing from single-A all the way up to Double-A and doing damage at every stop. The strikeouts are a wee bit concerning (~27% is a bit high for the minor leagues), but this is a Fun Player who will be Fun To Follow, especially if the big-league team continues to be disappointing. The Arkansas Travelers just got a lot more interesting!
This is definitely a quantity-over-quality trade with the Mariners taking chances on fringe players and a reliever who’s had a career-worst year, but moving Castillo out of the rotation (and moving his contract along with him) streamlines things for the Mariners. Still, that feels like a dispassionate way to discuss Castillo, who has been such a good Mariner over his time here, from mentoring the younger pitchers, to pitching in post-season games, to being a steady hand in the rotation last year when seemingly every pitcher went down for at least a while with some kind of injury. With the White Sox making a surprising run at the division title in a weak AL Central, theoretically Castillo will have an opportunity to play in the post-season again. But it does feel like the first brick to fall from a rotation that has so long been the core of the current team’s identity, with more moves possible. Change is hard. At least we have Boston Smith and his rec specs to see us through these trying times.
