Five Best Trade Fits for Mariners Starter Luis Castillo

Starting pitching remains at a premium this offseason, and as we enter the middle of December, the trade market is red-hot at the moment after several major trades went down this past weekend.

So, with numerous teams looking to add to their rotations and the trade market as active as ever, another name that could find himself on the move in the coming days or weeks is Luis Castillo.

There seems to be a consensus that money is tight in Seattle at the moment after a report from Adam Jude of The Seattle Times said that the $8 million in savings they recouped from non-tendering Josh Rojas, Sam Haggerty, Austin Voth and JT Chargois doubled the Mariners’ offseason budget.

So, given how deep Seattle’s current rotation is with Castillo, Logan Gilbert, George Kirby, Bryce Miller and Bryan Woo, it seems like the area where the M’s could afford to lose some talent to free up more payroll and/or improve the team without spending free agency prices.

Gilbert and Kirby are the Mariners’ most valuable starters, due to their immense skill and the fact that they’re only earning arbitration-level salaries. And Miller and Woo are still on pre-arbitration deals, so dealing them wouldn’t have any impact on the budget.

This means that Castillo, and the $24.15 million guaranteed yearly salary he holds through 2027, is a prime candidate for Jerry Dipoto and the Mariners’ front office to cash in on.

Castillo is well worth the investment for a contending team. He’s coming off a year in which he threw to a 3.64 ERA, a 3.91 FIP, a 1.17 WHIP and a .237 AVG against in 175.1 innings of work.

Looking at him from a more macro lens, he has been one of the league’s premier arms for several years now. He ranks eighth in MLB in starter fWAR since the beginning of the 2018 season. He’s thrown the sixth-highest amount of innings in that time span. And he’s posted six straight sub-4.00 ERA seasons, including a sub-3.00 ERA in 2022.

An important detail to note is that Castillo still holds a no-trade clause in his deal for one more season, meaning he’d need to approve the destination he’s dealt to should a trade come together this winter.

Furthermore, according to Ken Rosenthal of The Athletic, the Mariners would likely only look to move Castillo if it has an impact on their team now, meaning a move for big league talent.

So, with all that in mind, if Seattle is really looking to deal Luis Castillo, here are some of the top trade destinations for the 32-year-old righty.

New York Mets

The Mets have been the team of the offseason after winning the Juan Soto sweepstakes. But the consensus in Queens seems to be that the work isn’t done yet.

Starting pitching is an area the Mets could still consider upgrading in order to find that out-and-out ace to join the likes of Kodai Senga and Frankie Montas atop that rotation.

While the acquisitions of Montas and Clay Holmes are promising moves with immense upside that could be unlocked with the resources of the Mets’ pitching lab, they’re still both either reclamation or development projects.

And while Senga has flashed top-tier capabilities on the mound, after an injury-ridden 2024 season, he might not be the guy to hand the keys to the rotation just yet, especially for a team that’s looking to make another NL pennant push in 2025.

Castillo would do wonders in filling that ace role for a Mets team looking to keep up the form their rotation had when their fortunes turned around mid-season in 2024. They ranked top 10 in starter ERA (5th), WHIP (T-8th) and AVG against (T-4th) from June 1 onwards.

The Mets could satisfy the Mariners’ desire for a major league return and address their need for help at second base by starting negotiations around infielder Luisangel Acuña, who showed his worth in New York when filling in for Francisco Lindor after he went down with injury late in the regular season.

The near $25 million price tag that Castillo comes with would be no issue financially for the Mets and their deep-pocketed owner Steve Cohen, who has showcased his extreme willingness to spend since taking over majority ownership of the team in 2020.

Chicago Cubs

After trading for superstar outfielder Kyle Tucker this past Friday, the Cubs are in a unique position to capitalize on this acquisition and go all in in 2025.

Bringing in a top-end starter like Castillo could make a lot of sense for Chicago to take their starting rotation from good to great.

Shota Imanaga was excellent in his debut MLB season, finishing with a sub-3.00 ERA and placing fourth in NL Rookie of the Year voting. Fellow southpaw Justin Steele has posted an ERA under 3.20 in three consecutive seasons now.

But beyond those two, there are some considerable questions looming over the bottom three on the staff.

Jameson Taillon may’ve been a 3.27 ERA pitcher in 2024 but is only a year removed from being a near 5.00 ERA arm.

Newly acquired lefty Matthew Boyd was a saving grace for a Guardians team in desperate need of pitching down the stretch, but his success in 2024 was only over a small sample size (eleven starts in the regular season and postseason combined), and he too is just a year removed from a 5.45 ERA season in 2023 with Detroit.

And despite a sub-4.00 ERA season in 2024, Javier Assad still sported a 1.40 WHIP and .251 AVG against in the process.

By slotting in near the top, Castillo would help the Cubs address some of these concerns with the bottom half of their rotation, while also giving them a dominant top three that could go toe-to-toe with the best of the best in a postseason series.

The issue in a deal between the Mariners and the Cubs could fall with the major league pieces Seattle would receive in return.

Second baseman Nico Hoerner seems less likely to move now that the Cubs have freed up a space in the infield for prospect Matt Shaw by sending 3B Isaac Paredes to Houston. And while 1B/OF Cody Bellinger or OF Seiya Suzuki could give the Mariners the offensive boost they need at the first base/DH positions, both come with high price tags.

That means the Cubs would need to offer some additional financial relief to make any deal with the Mariners that included one of those names a possibility.

All that to say, the Cubs would bring both major league talent and a deep farm system to the table to negotiate a deal with the Mariners, it just may take more work than it would for the other teams listed here.

Baltimore Orioles

The Orioles are another team in need of a top-tier rotation piece after their ace Corbin Burnes became a free agent this winter.

Grayson Rodriguez and Zach Eflin provide this staff with a good foundation to build upon, but neither is the bona fide ace Baltimore needs to remain one of the American League’s top contenders.

And with Kyle Bradish still recovering from Tommy John surgery, the group beyond Rodriguez and Eflin, Dean Kremer, Albert Suárez, Trevor Rogers and Cade Povich, doesn’t necessarily provide an abundance of confidence for a team looking to make it further than the Wild Card round in 2025.

While their most recent signing, Tomoyuki Sugano, was a solid acquisition to make, the 2024 Central League MVP in NPB has yet to prove he can put up similarly impressive numbers (like a 1.67 ERA) in MLB.

Castillo would not only provide that ace-caliber arm, he would give a team that’s had such poor luck with starter health an extremely durable arm, who, as I mentioned earlier, ranks sixth amongst MLB starters in innings pitched since the start of 2018.

With Baltimore’s willingness to move current first baseman Ryan Mountcastle at the trade deadline, and now that Just Baseball’s No. 9 overall prospect, Coby Mayo, looks ready for his shot in the big leagues, Mountcastle could be a piece for the O’s to trade.

The Mariners may wish to build a deal around a hitter like Mountcastle, especially considering he only comes with an estimated $6.6 million price tag in 2025, plus an additional year of control in 2026.

Boston Red Sox

After acquiring Garrett Crochet from the White Sox during the Winter Meetings, the Red Sox could still stand to make another move for their rotation.

Unlike the other teams listed above, Boston has the luxury of having an ace in the fold already now that Crochet is on the roster.

However, Crochet only holds a roughly $3 million estimated salary for 2025, plus an additional arbitration year in 2026, meaning the Red Sox have a great financial opportunity to add another top-end option to their rotation and compete with the likes of some of the best rotations in the American League.

Castillo would add that buffer between Crochet and the rest of the rotation, which includes Tanner Houck, Brayan Bello and Kutter Crawford. All three had good years in 2024 but could be regression candidates in 2025.

Castillo’s excellent track record of durability would also give Boston an ace-caliber starter who could act as top-end injury insurance for Crochet, who’s already gone under the knife with Tommy John surgery in 2022, and that was before he became a full-time starter this past season.

The young 1B Triston Casas has had his name thrown around in trade conversations throughout the offseason so far and could be a perfect fit in Seattle.

The Mariners reportedly already rejected a Casas trade, but perhaps he could still be the centerpiece of a package if the Red Sox sweeten the deal. Boston has an intriguing farm system to deal from, making them a logical fit as a trade partner.

Detroit Tigers

While the other teams on this list have been connected to a Castillo trade by various sources, a team that hasn’t been commonly thrown around that could also use another top-tier starter is the Detroit Tigers.

Like Boston, Detroit has the ace role covered with 2024 AL Cy Young award winner Tarik Skubal already at the helm.

Yet, after Skubal, there are some serious questions facing the Tigers regarding their rotation in 2025.

Reese Olson had a strong start to 2024 but struggled in June, posting a 5.73 ERA before hitting the IL in July and then posting a 6.75 ERA in September upon his return to the mound.

The newly signed 37-year-old Alex Cobb looked good when he played last year, but only made three regular season starts due to injury.

Keider Montero had his moments in 2024 but was ultimately still a high-4.00s ERA guy in 2024. The former No. 1 overall pick in 2018, Casey Mize, has yet to find his footing in the big leagues. And Just Baseball’s No. 2 overall prospect, Jackson Jobe, has all the potential in the world but is still just 22 years old and only has yet to make an MLB start.

The Tigers had success with their pitching chaos approach last season, but that can’t be the blueprint to sustained success moving forward. That means a big-time pitching acquisition would be a smart move this winter, especially after seeing the impact Skubal had when he hit the mound every turn through the rotation last season.

Spencer Torkelson is a name that’s been tossed around in trade talks this winter, and while he can’t be the only name that heads Seattle’s way in a potential trade for Castillo, he could get the ball rolling by filling their need at first base at the major league level.

The Tigers also have an extremely deep farm system with six names in Just Baseball’s Top 100 prospect list that could supplement a return to the M’s.

Given the price of starters on the free agent market this winter, a $24.15 million annual salary for Castillo might be a cheaper price than Detroit would have to pay for some of the other rotation fits still available, like Sean Manaea, who Castillo is undoubtedly better than.