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Pre-deadline trades generally follow a template, with contenders filling needs by acquiring players from teams outside of the playoff races. Not every late July or early August deal fits into that pattern, however, and Saturday night brought a less common variety of trade, one between two American League teams striving for spots in the postseason field. The Mariners, who spent most of June atop the AL West but are now trying to claw their way back to the top of the division or at worst into a Wild Card slot, sent right-hander Luis Castillo to the AL Central-leading White Sox in exchange for reliever Seranthony Domínguez, outfielder Nolan Jones, and catching prospect Boston Smith.

While the players switching teams in this deal might fill some clear needs in their new locations, none of them offers a strong guarantee. Domínguez and Castillo both have high ERAs and messy peripherals this season, and Jones has been stashed in Triple-A all year after sub-replacement level performances in 2024 and ’25. Perhaps the most interesting aspect of this deal is that the White Sox are absorbing all of the money remaining on Castillo’s contract, which runs through the end of next season. The Mariners not only freed up some cash, which they may very well reallocate in the coming days, but they potentially opened up a spot in their rotation for Kade Anderson, the top pitcher on our recently updated Top 100 Prospects list, and added a prospect to their system. The ability to do so, while leaving behind an all-homegrown rotation that already includes three former first-round picks, speaks well of their vaunted pitching development program.

That said, it’s not hard to understand why Mariners fans might view this deal with some amount of cynicism and disappointment. After coming within one win of the franchise’s first trip to the World Series last October, the Mariners are 54-58, third in the AL West, three games behind the Astros (57-55), a game and a half behind the Rangers (55-56), and two games out of the third AL Wild Card spot, where seven teams — including the Tigers, who traded Tarik Skubal to the Dodgers on Saturday night — are within three and a half games. Our Playoff Odds put them at 47.7% at this writing, but if they don’t repurpose some of the savings from offloading Castillo’s salary, or come away from the deadline without something more exciting than middle relief and a prospect for their trouble, this will be remembered as a salary dump or even a white flag, not to mention an abrupt and bitter finish to a stretch in which the Mariners finally ended their postseason drought. The Mariners acquired Castillo from the Reds in a five-player blockbuster ahead of the 2022 traded deadline, and he not only helped them reach the playoffs after a 21-year absence but signed a a five-year, $108 million extension that was supposed to bring more glory than just one more trip to October.

It hasn’t been a great year for the 33-year-old Castillo. In fact, he’s in the midst of his worst season in terms of ERA (5.06), xERA (4.82), FIP (4.57), and strikeout rate (19.4%), with his 7.2% walk rate merely his highest since 2022 and his 1.44 homers per nine his highest since ’18, his second season in the majors. As recently as last year — his third in a row making at least 30 starts for the Mariners — he was quite solid, with a 3.54 ERA, 4.04 xERA, and 3.88 FIP all nearly identical to his 2024 marks, though his 21.7% strikeout rate represented a 2.6-point drop from that season.

Since coming over from Cincinnati, Castillo has decreased the use of his sinker in favor of his four-seamer, but the heat has waned, and the groundballs have disappeared. Where he had the majors’ highest groundball rate among qualifiers in 2021 (58.6%), Castillo is down to a career-low 36.3% this year:

Castillo’s 95.3 mph average velocity for his four-seamer is actually 0.3 mph higher than last year, but it’s down from 97.1 mph in 2022, and its results have gotten worse. Relative to last season, batters have increased their slugging percentage against it by 62 points:

As you can see, that increase is about twice the increase in expected slugging percentage against the four-seamer, and it’s not even Castillo’s biggest problem. Hitters have increased their slugging percentage against his slider by a honking 184 points, almost 100 ahead of their increase in xSLG against it, but where his whiff rates on the four-seamer have been stable from year to year, his whiff rate on the slider has fallen by 11 points since last year, and he’s become more vulnerable to lefties.

With Logan Gilbert, George Kirby, Emerson Hancock, and Bryan Woo all healthy from the outset of the season along with Castillo, the Mariners haven’t lacked for starting pitching. Indeed, once Bryce Miller rejoined the rotation in mid-May following an oblique strain that sidelined him during spring training, they expanded to a six-man rotation, though they also tried a modified five-man arrangement, with Castillo piggybacking after Miller on three occasions, and Miller following Castillo once. Despite announcing plans to involve the other starters in such a tandem arrangement, they instead kept with a six-man rotation.

Alas, the fact that the Mariners went just 9-15 in July, that they’ve spent just one day in first place since July 8 after sitting atop the division nearly uninterrupted since May 27, and that they’re now four games below .500 was not a great advertisement for any of the modified arrangements, particularly with other areas of the roster needing to be addressed. Suitors have reportedly shown interest in all of their starters, with The Athletic’s Ken Rosenthal and Will Sammon recently reporting that the team is open to moving the 27-year-old Hancock, who has pitched to a 3.26 ERA and 3.74 FIP and who still has four years of club control remaining. Prior to Saturday’s trade, the Seattle Times’ Ryan Divish and Adam Jude reported that Kirby could be moved in the right deal.

So even with the Castillo trade, it’s not out of the question that they trade another starter, because they have a pair of blue-chip starting pitchers in Double-A in Anderson and Ryan Sloan, who respectively placed third (as a 60-FV prospect) and 10th (as a 55-FV prospect) on our updated Top 100. The 22-year-old Anderson, a lefty who was the third pick of the 2025 draft out of Louisiana State University, has put up a 1.20 ERA and 1.88 FIP in 82.1 innings at Double-A Arkansas while striking out an ungodly 40.5% of hitters with four high-quality pitches and a deceptive delivery. The 20-year-old Sloan, a second-round pick in 2024 out of an Illinois high school, has posted a 3.74 ERA and 3.37 FIP with a 30% strikeout rate in 67.1 innings at Arkansas using a four-pitch arsenal that features a fastball that reaches triple digits.

There’s no guarantee either pitcher sees Seattle this season, but if the Mariners want to stick to a six-man plan, they have talented options available. In parting ways with Castillo, they’ve also shed the rest of his contract, meaning about $7.4 million remaining on this year’s $22.75 million salary, and the $22.75 million he’ll make next season. His deal also has a couple of options for 2028, one a $25 million vesting option if he reaches 180 innings in ’27 and doesn’t have an injury that would cause him to start ’28 on the injured list, as well as a conditional $5 million club option if he’s on the IL for more than 130 consecutive days during 2025-27 due to Tommy John surgery or an operation stemming from damage to his UCL.

As he joins the White Sox — who are in the midst of a remarkable turnaround from their record-setting 121-loss season in 2024, sitting atop the AL Central with a 58-52 record and a three-game lead over the Guardians — the presumption is that Castillo will bump rookie Noah Schultz, who’s carrying a 5.82 ERA, out of the rotation. Righties Sean Burke and Davis Martin are both in the midst of breakout seasons, with the former putting up a 3.04 ERA and 3.29 FIP (both seventh among AL qualifiers) and the latter a 3.62 ERA and 3.12 FIP (respectively 12th and fifth in the AL). Behind them, things get shaky. Lefty Anthony Kay has a 4.25 ERA but a 4.94 FIP, while righty Erick Fedde has a 4.13 ERA and a 5.34 FIP, with manager Will Venable using him behind an opener in 10 of his 22 appearances.

As for the 31-year-old Domímguez, this is the third time in as many seasons that he’s been dealt in late July or early August. On July 26, 2024, he was traded by the Phillies (who had signed him out of the Dominican Republic in 2011) to the Orioles along with Cristian Pache in exchange for Austin Hays, and then on July 29, 2025 he was traded by the Orioles along with cash to the Blue Jays for Juaron Watts-Brown. In Baltimore, he took over closer duties from the struggling Craig Kimbrel (who was released before the end of the season) and helped them secure a Wild Card berth, while in Toronto, he served in a setup role and helped the Blue Jays reach the World Series.

In late January, the White Sox signed Domímguez to a two-year, $20 million deal that includes a $12 million mutual option for 2028 with a $2 million buyout. He began the season as the closer, but blew five out of 17 save opportunities before being displaced from the role in late June. Since then, Venable has spread the ninth-inning duties around, with righty Grant Taylor notching three saves, lefty Sean Newcomb two, and lefties Bryan Hudson and Tyler Schweitzer one apiece. Domínguez has pitched to a 3.99 ERA and a 4.64 FIP, with a career-worst (if only slightly) 13.9% walk rate and a beefy 1.41 homers per nine offsetting his 28.5% strikeout rate. He walked 13.8% of hitters last year, up from 8.2% in 2024. He owes that skyrocketing walk rate largely to last year’s addition of a splitter; while he’s generating a 57.8% whiff rate with the pitch, the problem is that more often than not batters aren’t swinging at it. He’s landing the pitch in the strike zone just 30.8% of the time, and hitters are chasing it out of the zone only 29.6% of the time, down from 39.6% last year. Both of our pitch modeling systems still regard his stuff as very good, but his command and location as lacking; we’ll see if the Mariners can get more out of him than the White Sox did.

Jones hit for a 137 wRC+ with 3.8 WAR in just 106 games for the Rockies in 2023, but it’s been mostly downhill for him since then. Recurring lower back woes and a left knee injury cost him about two and a half months in 2024, and he hit just .227/.321/.320 (69 wRC+) with three homers and -0.9 WAR in 79 games. The Rockies traded him back to the Guardians — who drafted him in the second round in 2016 and traded him to the Rockies in November 2022 — in March 2025 in exchange for Tyler Freeman. His struggles continued, as he batted .211/.296/.304 (72 wRC+) with five homers and -0.4 WAR in 136 games. In late March, Cleveland outrighted him to Triple-A Columbus, and on June 11, they traded him to Chicago for $250,000 in international bonus pool money. Jones spent all of his time in the White Sox organization with Triple-A Charlotte without being added to Chicago’s 40-man roster; at the two International League stops, the now-28-year-old hit a combined .257/.362/.445 (107 wRC+).

With Seattle, Domínguez will probably slot in as a middle-innings guy, lower in the pecking order than lefties Gabe Speier and José A. Ferrer and righty Eduard Bazardo as well as closer Andrés Muñoz. Jones figures to remain a depth piece even if the team does move pending free agent Randy Arozarena, an All-Star who’s of particular interest in a market short of right-handed bats; of course, the Mariners are looking for them, too.

As for Smith, he’s a lefty-swinging 23-year-old who has rocketed from A-level Kannapolis through High-A Winston-Salem to Double-A Birmingham this season while hitting a combined .291/.448/.589 (167 wRC+), albeit with a 27.7% strikeout rate. He does not yet have a prospect grade from our team, but Eric Longenhagen did pass along these notes:

Smith was a high-priority senior sign out of Wright State in 2025, as the Nationals reached for the 25-homer catcher in the fifth round to lock in the leverage-less lefty stick for just $50,000. Washington traded Smith to the White Sox for Curtis Mead before Smith had even played an official game for them, and Smith has moved through the minors very quickly, reaching Double-A and clubbing 22 homers in 78 games before he was sent to Seattle.

At a hard-swinging 5-foot-10, Smith has a selective approach and above-average big league power right now (112 mph max exit velocity this year, 49% hard-hit rate, 107 EV90). His swing is geared for pull and launch in the extreme (20 degrees of launch on average) at the cost of contact on the outer half of the zone. Smith isn’t a good defensive catcher. He’s a fair receiver at the bottom of the zone but poor along the other three edges, and his throwing and ball blocking are also below average. He needs work on defense in order to be a viable big league defender. Should he need to move to first base, his strikeouts are excessive. It’s sink or swim for him at catcher, and he’s now in a system that has had some success at developing guys in these regards, most notably the freshly-signed, high school version of Harry Ford.

Castillo isn’t an ace, but he helps bulk up the White Sox rotation. The glass-half-full view from the Mariners’ side is that trading him gives Seattle some room to take bigger swings as the deadline approaches — and after, if they do call up either Anderson or Sloan. With Skubal being dealt, this wasn’t the biggest trade pulled off by an AL Central team on Saturday night. By the time the trade deadline passes, it may not be the biggest made by either of these contenders.