Mariners Showing Interest In Willi Castro, Twins’ Relievers

The Mariners have already upgraded the right side of their infield with last week’s addition of Josh Naylor, and as they continue to look around the league for help at the other corner and in the bullpen, they’ve increasingly focused in on the Twins, reports Daniel Kramer of MLB.com. Seattle had interest in Willi Castro this past offseason and has again been in touch with Minnesota about the possibility of a Castro swap.

Castro, 28, would give the Mariners an option at third base while still leaving the door open for a potential addition of a prominent slugger like Eugenio Suárez. The switch-hitting Castro is versatile enough to handle second base, shortstop or any of the three outfield spots — though he’s best used as an emergency option at short or in center. He’s primarily played second base and the outfield corners for the Twins this season but has 74 innings at third base (532 in his career) and 26 innings at short (1213 career innings).

The versatile Castro is in his final season of club control and earning $6.4MM. He’s hitting .252/.343/.418 with 10 homers, 15 doubles, a pair of triples and nine steals (in 12 tries). It’s Castro’s third straight productive season since being non-tendered by the Tigers and signing a minor league deal in Minnesota. In two-plus years with the Twins, he’s slashed .251/.336/.401 while playing all over the diamond.

Castro has been solid enough at the plate that even absent a more notable acquisition at the hot corner, he’d still be a marked improvement over in-house options on his own. Rookie Ben Williamson has been playing third base for much of the season in Seattle. He’s turned in sharp defense but carries an anemic .256/.293/.315 batting line in 289 turns at the plate. The hope had been that Jorge Polanco could play third base for the M’s after re-signing this past offseason, but he’s been limited to DH work for much of the season after undergoing knee surgery following the 2024 campaign and playing through a side/oblique issue for much of the early portion of the current season.

On top of their need in the infield, the Mariners have been canvassing the trade market for high-leverage relief help. Kramer notes that hard-throwing righties Jhoan Duran and Griffin Jax stand out as on-paper fits and the type of arms Seattle has been seeking. Both are in their first arbitration season and controlled through 2027. Duran is earning $4.125MM this season. Jax is being paid $2.365MM.

While Duran is the more famous of the pair given his status as Minnesota’s closer and his possession of one of MLB’s hardest fastballs, both pitchers are viewed within the industry as elite bullpen options. Duran carries a career 2.47 ERA and 30.6% strikeout rate, though this year’s 25.7% mark (while still strong) is a career low. He’s averaging 100.2 mph on his four-seamer and complementing that blistering offering with a splitter/sinker hybrid (“splinker”) that sits 97.5 mph.

Duran may be more well-known, but Jax is arguably even more appealing. Beyond his lower salary, he boasts superior strikeout and walk rates, sitting at 36.9% and 6.7%, respectively. He’s been dogged by a .371 average on balls in play, which has helped to inflate Jax’s ERA to 3.91, but metrics like FIP (2.00) and SIERA (1.94) rank him among the game’s very best relievers. Among the 651 pitchers (starters and relievers alike) to throw even five innings in the majors this year, Jax is tied with Aroldis Chapman for the fourth-best swinging-strike rate (19.8%). Josh Hader, Mason Miller and Fernando Cruz are the only pitchers with higher marks.

Adam Jude of the Seattle Times writes that while the Mariners indeed covet Duran and/or Jax — as well as Castro — there’s very little chance the M’s could pry away both Castro and one of the Twins’ top bullpen arms in the same trade. ESPN’s Jeff Passan reported last week that the Twins were seeking multiple top-100 prospects for either Duran or Jax individually. Jude hears similarly. Adding Castro, one of the more appealing rental players on the market, would only drive the asking price up even further.

Jude suggests left-hander Danny Coulombe as one viable alternative in the Minnesota bullpen. He’s pitched 31 innings this year and logged a pristine 1.16 ERA with a 25.4% strikeout rate and 7.4% walk rate. The 35-year-old southpaw signed a one-year, $3MM deal with the Twins over the winter — his second stint in Minnesota — and is a free agent at season’s end.

Speculatively, the Mariners could also look into righty Brock Stewart. The 33-year-old is making just $870K this season and, like Duran and Jax, is controlled through 2027. He’s been excellent since signing a minor league deal with the Twins three years ago but has also missed considerable time due to injury. Stewart touts a 2.33 ERA, 31.7% strikeout rate and 9.5% walk rate in 77 1/3 innings dating back to Opening Day 2023. Stewart is averaging 96.1 mph on his four-seamer, and while his 15.1% swinging-strike rate isn’t quite at Jax’s elite level, it’s tied with San Diego’s Jason Adam for 28th among 373 big league pitchers who’ve pitched at least 30 innings this year.

The Mariners are well-positioned to land virtually any trade target they covet — it’s just a matter of how much they’re willing to thin out what’s regarded as one of baseball’s top farm systems. Seattle has eight of Baseball America’s top-100 prospects. Minnesota isn’t embarking on a full rebuild but rather aiming to retool and contend again in 2026, so they’d probably prefer prospects closer to big league readiness for their top trade chips (though they did settle on a 19-year-old catching prospect in yesterday’s Chris Paddack trade).