The Seattle Mariners have executed a strategic roster move to enhance their pitching depth by acquiring right-handed pitcher Cooper Criswell from the New York Mets in exchange for cash considerations. This transaction prompted the immediate designation for assignment of left-handed pitcher Jhonathan Díaz, ensuring the Mariners maintain a full 40-man roster.
Cooper Criswell Brings Versatility to Mariners Pitching Staff
Criswell joins the Mariners as a pitcher with proven Major League experience, capable of handling innings in various roles. While his specific role with Seattle has not been immediately defined, his addition is particularly valuable for a team that boasts a strong starting rotation but seeks to bolster its depth beyond the core starters.
The Mariners' front office appears focused on acquiring reliability and experience over untapped potential, emphasizing the need for a safety net to support both the rotation and bullpen as the season progresses. This move underscores Seattle's careful approach to roster management and flexibility.
Criswell's Recent Performance and Career Highlights
Cooper Criswell, 29 years old, appeared in seven Major League games for the Boston Red Sox in 2025, including one start, compiling a 1-0 record with a 3.57 ERA over 17.2 innings. The Mets claimed him off waivers from Boston on December 5, 2025, but designated him for assignment on January 21, 2026.
His most substantial Major League season came in 2024 with the Red Sox, where he pitched 99 1/3 innings across 18 starts and eight relief appearances, finishing with a 4.08 ERA. During that season, Criswell demonstrated a 17.2% strikeout rate, a 7.2% walk rate, and induced ground balls on 50.3% of balls in play.
Seattle Mariners Current Pitching Rotation and Depth
The Mariners' starting rotation is anchored by veteran Luis Castillo and features Logan Gilbert, George Kirby, Bryan Woo, and Bryce Miller. This group is widely regarded as one of the premier rotations in Major League Baseball.
Beyond the primary starters, Seattle's pitching depth includes Logan Evans, Emerson Hancock, and Blas Castano, all of whom are working to establish themselves at the Major League level. Prospect Jurrangelo Cijntje remains in the developmental pipeline, having made only seven starts in Double-A without yet reaching Triple-A.
Mariners Bullpen Composition and Roster Challenges
The Mariners' bullpen is projected to include eight key arms: Andrés Muñoz, Matt Brash, Jose A. Ferrer, Eduard Bazardo, Gabe Speier, Carlos Vargas, Casey Legumina, and Jackson Kowar. Among these relievers, only Brash and Ferrer retain minor league options, though both are considered too valuable to be demoted.
This limited flexibility presents potential challenges for Criswell, who may be utilized as a long reliever but could face roster complications if the team attempts to pass him or another reliever through waivers.
Jhonathan Díaz Designated for Assignment
In the corresponding roster move, left-handed pitcher Jhonathan Díaz was designated for assignment. The 29-year-old appeared in one Major League game for Seattle in 2025 but spent the majority of the season with Triple-A Tacoma.
At Tacoma, Díaz pitched 138 2/3 innings, posting a 4.15 ERA with a 19.8% strikeout rate and a 4.1% walk rate. Over five Major League seasons, his career totals include 46 1/3 innings pitched with a 4.66 ERA.
