The Mariners’ decision to move Luis Castillo in the Seranthony Domínguez deal looked like a clean bit of roster management at the time. Seattle had too many arms, needed to clear space for phenom prospect Kade Anderson, and Castillo was the obvious name to send out the door. He was the most expensive starter in the mix, offered the least upside, and was in the middle of the worst regular season of his career.
In his final 20 appearances as a Mariner, Castillo put up a 5.06 ERA with a 4.58 FIP over 99.2 innings. Seattle shipped him to the White Sox and got Nolan Jones, Boston Smith and Domínguez back.
The salary relief made sense. The return, less so.
Smith has been the most intriguing piece in that package, but his Arizona Fall League showing has not helped the Mariners feel better about the deal. The 2025 sixth-round pick out of Wright State University was originally drafted by the Nationals, then traded to Chicago at the start of last season for Curtis Mead. He was productive in his first year as a pro, turning in a .990 OPS across 493 plate appearances, including 243 in Double-A split between the Birmingham Barons and the Arkansas Travelers.
He has mostly worked behind the plate, while also seeing some time in the outfield. He is not a finished product and not yet a true dual threat like a Daulton Varsho, but scouts have liked the athleticism he has shown since college. Seattle has him ranked as its No. 13 prospect, and he backed that up with a 136 wRC+ over 146 plate appearances with Double-A Arkansas.
That promise has not carried over to Peoria. In the AFL, Smith is hitting just .146/.323/.188 in 62 plate appearances.
The on-base skills are still there to a degree, but the overall line is ugly, and the strikeout rate tells the story: 19.4% walks, 33.9% strikeouts. His passive approach has become the issue again.
Last year in Double-A, Smith swung at only 39.6% of pitches, which placed him in the 7th percentile. That kind of patience can work when pitchers are missing the zone, as they often do in the minors.
Against better arms, though, it can turn into a problem fast. In the AFL, and eventually at Triple-A and in the majors, that kind of approach can leave him exposed.
The temptation is to say he simply needs to be more aggressive, but the issue appears more complicated than that. Scouts say Smith does a good job identifying pitches he can pull in the air, and that showed up on 19.3% of his batted balls.
The concern is that he may lean on that skill too heavily instead of building on it. That level of selectivity could also point to a lack of confidence when he can’t fully tap into his power.
It is still too early to rewrite the book on him based on a small AFL sample. Even so, this stretch has given a clearer look at the flaw that could define his climb through the system. Seattle kept pushing him upward, and now the question is whether he can adjust or whether that same weakness will keep catching up to him.
In Other News...
Mariners Suddenly Have A Rookie Storyline Fans Cant Ignore
Kade Anderson has gone from a fast-rising name in the system to one of the more intriguing pieces of the Mariners near future. After leading all minor league pitchers with a 1.06 ERA and a 0.643 WHIP in 2026, he also gave Seattle a glimpse of what might be coming when he was called up in August and held his own in seven major league starts.
The bigger buzz now is what comes next. Steamer sees Anderson making 24 starts for Seattle in 2027 with a 3.28 ERA, which would put him right in the mix with the clubs most established arms, and his limited big league service time means he still projects as a rookie next season. That combination makes him a legitimate AL Rookie of the Year candidate and gives the Mariners another storyline worth watching closely as their rotation picture keeps taking shape. [Read more 🡒]
Pirates Just Gave Up On A Reliever Another Team Clearly Wants
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Mattson arrives with a recent track record that suggests there is something to work with, even after a rougher follow-up season in Pittsburgh. Seattle will get a chance to evaluate whether adjustments can help him rediscover the effectiveness he showed the year before, and he should be in the running for a bullpen job when camp opens. [Read more 🡒]
Cole Youngs Next Step Could Matter More Than His Gold Glove
Cole Youngs first Gold Glove arrived with the kind of recognition every young infielder wants, but the award may only be the start of the conversation around his value to Seattle. The Mariners second baseman was honored as the American Leagues best at the position, becoming the third Seattle second baseman to win the award, and he pointed to the people who helped get him there, including former infield coach Perry Hill and his father.
Even with the hardware in hand, Young is already talking like a player focused on what comes next. He said his offseason work will center on getting stronger and becoming more versatile, a useful mindset for a Mariners infield that could use flexibility as it maps out the months ahead. For Seattle, the Gold Glove is a nice milestone, but Youngs next step may end up mattering even more. [Read more 🡒]