The Seattle Mariners have continued their tradition of aggressive pitching staff management, officially announcing that the Mariners acquire RHP Cooper Criswell from the New York Mets. The deal, which was finalized this week, sees the right-handed pitcher head to the Pacific Northwest in exchange for cash considerations. To facilitate the move and clear a spot on the 40-man roster, the Mariners designated left-hander Jhonathan Diaz for assignment.
The Mechanics of the Trade
In a move designed to provide immediate organizational depth, the Mariners targeted Cooper Criswell, a versatile arm who has shown the ability to function both as a starter and a long-reliever. The New York Mets, who had recently brought Criswell into the fold, opted to move the right-hander for cash, allowing Seattle to secure a pitcher who fits their specific developmental profile.
Cash Considerations and Roster Moves
While the specific dollar amount has not been disclosed, the trade is a straightforward exchange of cash for talent. This type of transaction is common during the offseason as teams look to balance their 40-man rosters. For Seattle, the acquisition meant sacrificing a roster spot currently held by Jhonathan Diaz. Diaz, a 29-year-old southpaw, now enters the waiver process, where he could be claimed by another club or potentially remain in the Mariners' system if he clears.
Who is Cooper Criswell?
Standing at 6-foot-6, Criswell provides a unique look for opposing batters. Now 29 years old, the right-hander has navigated several organizations, refining a pitch mix that relies heavily on command and movement rather than overwhelming velocity. His ability to induce ground balls and limit hard contact has made him an intriguing target for a Mariners front office that has a proven track record of maximizing the potential of veteran arms.
Arsenal and Physical Profile
Criswell’s effectiveness stems from a heavy sinker and a sweeping slider that keeps hitters off-balance. Because of his height and release point, his pitches often have a deceptive plane that makes it difficult for hitters to square up the ball. In the modern MLB landscape, where pitching depth is often the difference between a postseason berth and an early October exit, Criswell represents a "glue guy" for the staff who can eat innings in various roles.
Analyzing Recent Performance: 2025 vs. 2024
To understand what the Mariners are getting, it is essential to look at Criswell's recent workload. During the 2025 season, Criswell had a limited sample size, appearing in seven games for the Boston Red Sox. While those seven appearances provided a glimpse of his current form, his 2024 campaign stands as his most recent full season of work and a better indicator of his overall utility. During that 2024 season with Boston, Criswell proved he could handle a significant workload, alternating between the rotation and the bullpen as a reliable swingman. For the Mariners, having a player with recent American League experience is a calculated move to ensure they have reliable options should injuries strike their primary rotation.
Strategic Fit in the Seattle "Pitching Lab"
The decision to acquire RHP Cooper Criswell aligns perfectly with Seattle's broader organizational philosophy. Under the leadership of Jerry Dipoto and Justin Hollander, the Mariners have become known as a "pitching lab," consistently identifying pitchers with specific traits—such as high horizontal break or unique release points—and helping them refine their arsenals to achieve career-best results.
Depth and Flexibility
Criswell joins a Mariners pitching staff that is already considered one of the most formidable in the American League. With a rotation led by stars like Luis Castillo, George Kirby, and Logan Gilbert, Criswell is not expected to carry the load at the top of the order. Instead, he projects as a high-floor depth option who can shuttle between Triple-A Tacoma and the Major League roster as needed. His presence allows the Mariners to be more flexible with their younger prospects, ensuring they aren't rushed into high-leverage situations prematurely.
Roster Consequences: Jhonathan Diaz Designated for Assignment
To make room for Criswell on the 40-man roster, the Mariners had to make a difficult decision regarding Jhonathan Diaz. The left-hander was designated for assignment (DFA), a move that places him on waivers. Diaz has provided depth for the Mariners in the past, but the team ultimately decided that Criswell’s right-handed profile and his specific experience in the American League provided more value over the course of the 162-game grind.
What Happens Next for Diaz?
When a player is DFA'd, the team has seven days to trade him or place him on irrevocable waivers. If Diaz clears waivers, he can be sent outright to the minor leagues, though players with enough service time may have the right to elect free agency. The Mariners will monitor this situation closely as they finalize their pitching depth charts heading into spring training.
Looking Ahead to Spring Training
For the New York Mets, this trade represents a minor consolidation of their roster as they continue to reshape their pitching staff. By recouping cash, the Mets gain a small amount of flexibility for future moves as the spring training period approaches. For Seattle, the focus remains on the American League West crown. By adding Cooper Criswell, they have successfully reinforced their floor. Fans can expect to see Criswell competing for a role in the bullpen or as a sixth-starter option when the team congregates in Peoria for spring training.
Sources & Original Reporting
