A closer look at Mariners’ haul from Luis Castillo trade

The Luis Castillo era is officially over in the Pacific Northwest.

The Seattle Mariners traded their veteran right-hander to the Chicago White Sox on Saturday for the three-player haul of reliever Seranthony Domínguez, outfielder Nolan Jones and catcher/outfield prospect Boston Smith.

Watch: Shannon Drayer breaks down Mariners’ Luis Castillo trade

Here’s a closer look at the three players the Mariners received in return for Castillo.

Seranthony Domínguez

The 31-year-old Domínguez adds a power arm to the Mariners’ bullpen and figures to slot in as a middle reliever with potential to cover some high-leverage spots.

Domínguez’s velocity and ability to generate swing and miss are his standout traits.

He averages 97.3 mph on his fastballs (a four-seamer and sinker), which ranks in the 90th percentile in the league. He’s sporting a 38.5% strikeout rate (88th percentile) and 29.6% whiff rate (80th percentile). Since the start of the 2025 season, Domínguez’s 29.6% strikeout rate ranks 25th among qualified relievers, one spot behind Mariners left-hander Gabe Speier (29.7%).

The right-hander generates a solid 24.3% whiff rate on his four-seamer and has three off-speed pitches to put batters away with. The sweeper is Domínguez’s go-to off-speed pitch and he throws it to both righties and lefties. Batters are hitting .200 against it with a 32.2% whiff rate this year. However, his splitter and rarely used curveball, both of which are used almost exclusively against left-handed batters, have been his most effective. Batters are hitting .111 with a 57.1% whiff rate against his splitter. The curveball, which he’s thrown just 15 times, has a 66.7% whiff rate.

Domínguez is toughest against right-handed batters, holding them to a .178 average and .587 OPS with three homers in 84 plate appearances this season, and a .179 average over the course of his career.

Command can be an issue for the Esperanza, Dominican Republic, native. He’s currently running a career-worst 13.9% walk rate, the eighth-highest mark among qualified relievers in 2026. His 13.8% walk rate since the start of last year is also third worst among relievers. He was also tied for the most wild pitches in MLB last season with 12.

Nolan Jones

Jones, who has spent all of this season in Triple-A, was a bit of a surprising acquisition for the M’s since he’s a left-handed hitting corner outfielder, but he provides some outfield depth and could make his way to the 26-man roster if Luke Raley’s IL stint ends up being a lengthy one.

The 28-year-old outfielder finished fourth in National League Rookie of the Year voting with the Colorado Rockies back in 2023 when he hit .297 with a .389 on-base percentage, .931 OPS, 20 homers, 22 doubles and 20 stolen bases. Jones wasn’t just a Coors Field merchant that season either, as his home and road splits were pretty much the same. But he hasn’t been a productive player since and was one of baseball’s worst hitters last season with a 72 wRC+ that was tied for the seventh-worst mark among players with at least 400 plate appearances.

There arm some traits to like with Jones, particularly his elite arm strength. He led baseball in arm strength in 2023 while averaging 98.9 mph on the top 10% of his throws and maxed out at 102.7 mph. The former second-round pick has also shown some ability to hit the ball hard, limit chase and work walks during his time in the majors. He even had an above average hard-hit rate (46.7%) and walk rate (9.7%) during his struggles in 2025.

The arm strength hasn’t translated into Jones being a good defender, though. He posted negative outs above average in each season and negative defensive runs saved twice from 2023-25. His strengths at the plate have also been overshadowed by his lack of contact. Even in his strong 2023 campaign, he ranked in both bottom 15 percentile in whiff rate, strikeout rate and squared-up contact.

Boston Smith

The 23-year-old Smith was Chicago’s No. 15 prospect at the time of the trade and is now ranked as the No. 14 prospect in the Mariners’ organization, according to MLB Pipeline.

A left-handed bat, Smith is listed as catcher/outfielder but has experience playing all over the field, having manned every position except first base and pitcher between his time at Wright State and playing in college summer leagues.

Smith’s power and patience standout most. He clubbed a school-record 26 homers as a senior at Wright State in 2025 and has hit 22 over 79 games this year in his first season of professional baseball, which has spanned across three levels of the minor leagues (Single-A, High-A and Double-A). And he’s sporting a 21.3% walk rate this year, tied for the eighth-best mark among minor leaguers in Single-A or above.

Seattle Mariners news and more

• Mariners place OF Luke Raley on injured list, call up Seattle native
• Report: Teams getting sense M’s George Kirby available in trades
• Seattle Mariners unveil expected return date for Brendan Donovan

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