Lead: The Seattle Mariners have acquired right-hander Cooper Criswell from the New York Mets in exchange for cash considerations, the club announced in late January 2026. The move follows Criswell’s designation for assignment after the Mets added Freddy Peralta and Tobias Myers; Seattle designated left-hander Jhonathan Díaz as the corresponding roster move. Criswell, 29, profiles as a swingman or back-end starter with the most extensive MLB action coming in 2024 with Boston. The transaction aims to add experienced depth to a Mariners staff already led by a strong five-man rotation.
Key Takeaways
- Seattle acquired RHP Cooper Criswell from the Mets for cash considerations; the Mariners designated LHP Jhonathan Díaz for assignment in the corresponding move.
- Criswell, 29, logged 99 1/3 innings for Boston in 2024 (18 starts, eight relief appearances) and posted a 4.08 ERA with a 17.2% strikeout rate and 7.2% walk rate.
- In 2025 Criswell spent most of the year in Triple-A (65 2/3 IP, 3.70 ERA, 24.5% K rate, 10.1% BB rate), and he exhausted his final minor-league option that season.
- The Mariners currently project a top five of Logan Gilbert, George Kirby, Bryan Woo, Bryce Miller and Luis Castillo, leaving depth beyond that group thin.
- Seattle’s bullpen already looks crowded on paper with an eight-man projection that limits option flexibility; Criswell could slide into a multi-inning relief role or compete for swingman starts.
- Díaz, 29, has 46 1/3 career MLB innings with a 4.66 ERA and has often spent extended time in Triple-A; he will clear DFA waivers or be the subject of trade interest for up to five days.
- Criswell agreed to a $800,000 guarantee for 2026 with Boston last November, only slightly above the projected $780,000 MLB minimum for 2026.
Background
Cooper Criswell first reached sustained big-league innings in 2024 with the Boston Red Sox, making 18 starts and multiple relief appearances. His 2024 profile combined moderate strikeout ability (17.2% K rate) with strong contact management—he limited walks to 7.2% and generated a 50.3% ground-ball rate. Those attributes fit the swingman/back-end starter mold teams value: someone who can eat innings in various roles while helping limit hard contact.
Roster churn and acquisitions pushed Criswell down Boston’s depth chart in 2025. The Sox added Garrett Crochet, signed Walker Buehler and regained Lucas Giolito from injury, shrinking opportunities for fringe rotation options. Criswell spent most of 2025 in Triple-A, where his strikeout rate rose to 24.5% but his walk rate also climbed to 10.1%, an uneven profile that left him on the fringes of a big-league roster.
Main Event
On the heels of New York acquiring Freddy Peralta and Tobias Myers from Milwaukee, the Mets designated Criswell for assignment. Seattle moved quickly to secure him, sending cash to New York in the reported deal and placing Jhonathan Díaz on DFA as the corresponding transaction. Reporting on the move was first attributed to Jorge Castillo of ESPN, while local coverage in Seattle noted cash considerations changed hands.
The roster mechanics matter: Criswell exhausted his final minor-league option in 2025, and Boston had previously guaranteed him $800,000 for 2026 when he accepted a deal to avoid immediate free agency. Despite that guarantee, he was exposed to waivers twice—designated by Boston in December, claimed by the Mets, then DFA’d again after New York’s recent additions. Seattle evidently judged Criswell worth claiming or acquiring rather than waiting for him to clear.
Jhonathan Díaz, designated by Seattle, has a limited MLB track record—46 1/3 innings across five seasons with a 4.66 ERA—and spent most of 2025 in Triple-A Tacoma, where he logged 138 2/3 innings and posted a 4.15 ERA. The Mariners will have up to five days to trade Díaz or place him on waivers; if he clears, he could elect free agency because of a prior outright.
Analysis & Implications
On paper the Mariners’ frontline rotation is one of the American League’s better groups, headlined by Logan Gilbert, George Kirby, Bryan Woo, Bryce Miller and Luis Castillo. That excellence at the top increases the value of versatile depth: teams with top-end starters still need swingmen to bridge innings, spot-start and absorb injuries across a 162-game season. Criswell’s profile—experience as both starter and reliever, ground-ball tendencies—addresses that need.
However, roster fit is tight. Seattle’s relief corps already projects to eight arms, many of whom lack minor-league options. That limited flexibility raises questions about where Criswell will be used and whether the club will need to make subsequent moves to create optionable depth. If Criswell stays on the active roster he provides multi-inning relief and could spot-start; if Seattle tries to pass him through waivers, roster churn may follow.
Financially the acquisition is low-risk for Seattle: cash was exchanged rather than a prospect, and Criswell’s guaranteed $800,000 for 2026 is marginally above league minimum. From Criswell’s perspective, his prior outright gives him leverage to elect free agency if he clears waivers, though doing so would require forgoing guaranteed pay—an important practical constraint for a pitcher with under five years of MLB service time.
Comparison & Data
| Player / Year | Level | IP | ERA | K% | BB% | GB% |
|---|---|---|---|---|---|---|
| Cooper Criswell (2024) | MLB (BOS) | 99 1/3 | 4.08 | 17.2% | 7.2% | 50.3% |
| Cooper Criswell (2025) | AAA | 65 2/3 | 3.70 | 24.5% | 10.1% | 49.4% |
| Jhonathan Díaz (MLB career) | MLB | 46 1/3 | 4.66 | 15.1% | 12.3% | 45.2% |
| Jhonathan Díaz (2025) | AAA Tacoma | 138 2/3 | 4.15 | 19.8% | 4.1% | 46.9% |
The table highlights contrasts: Criswell’s Triple-A 2025 strikeout rate rose relative to his 2024 MLB mark, but also showed a higher walk rate, suggesting improved swing-and-miss potential accompanied by control volatility. Díaz’s larger workload in Triple-A in 2025 produced a better strikeout-to-walk balance than his limited MLB samples, but his major-league track record remains small and uneven.
Reactions & Quotes
“Mariners acquiring Cooper Criswell,”
Jorge Castillo, ESPN (reporting)
“Cash considerations were involved in the transaction,”
Ryan Divish, The Seattle Times (reporting)
“Díaz was designated as the corresponding roster move, opening the spot for Criswell,”
Team announcement (Mariners)
Each short statement above reflects reporting and team transaction notes; local beat writers and the club released the basic mechanics while evaluators noted the roster-fitting issues described earlier.
Unconfirmed
- It is unconfirmed whether the Mariners intend to attempt to pass Criswell through waivers later to create roster flexibility; no official plan has been announced.
- Reports differ on whether Jhonathan Díaz retains a bona fide fourth minor-league option; club sources have not confirmed his exact option status.
- Any internal plans for using Criswell as a long reliever versus a rotational depth option remain speculative until Spring Training usage patterns emerge.
Bottom Line
The Mariners’ acquisition of Cooper Criswell is a low-cost move to bolster experienced pitching depth. Criswell’s mix of starting and relief experience, ground-ball tendencies and recent Triple-A workload make him a logical candidate for multiple roles, even if the roster logjam forces additional moves.
For Seattle the key questions are role clarity and roster flexibility: will Criswell carve out a multi-inning relief niche, spot-start when needed, or become a transactional piece shuffled through waivers? In the near term the transaction improves margin-of-error for the rotation; in the longer term it will be judged on how Criswell either stabilizes innings or provides tradable short-term value.
Sources
- MLB Trade Rumors — media report on the transaction
- Jorge Castillo / ESPN (Twitter) — initial reporting credited to ESPN reporter
- Ryan Divish / The Seattle Times — local beat reporting on roster mechanics