(Image Source – Getty Images) The Seattle Mariners made a simple yet significant move to boost their pitching depth by bringing in Cooper Criswell from the New York Mets in exchange for cash. This trade quickly altered the roster’s back end, leading to lefty Jhonathan DÃaz being designated for assignment to maintain a full 40-man roster. Criswell joins the team as a pitcher who has shown he can manage Major League innings, even if his exact role isn’t defined right now.This is important for a Seattle team that relies on a solid starting rotation but has less depth after that. The front office is definitely focusing on reliability and experience rather than potential. This decision is more about bolstering the safety net for the rotation and bullpen than just filling a gap. It also shows how carefully Seattle is handling roster flexibility as the season progresses.
How Cooper Criswell balanced starting and relief roles for the Boston Red Sox in 2024
Criswell, 29, played in seven Major League games (one of which was a start) in 2025 for the Boston Red Sox, finishing with a record of 1-0 and a 3.57 ERA over 17.2 innings. He was picked up off waivers by the Mets from Boston on December 5, 2025, but was designated for assignment on January 21, 2026.His biggest season in the big leagues happened in 2024 with Boston, where he pitched 99 1/3 innings across 18 starts and made eight relief appearances, finishing with a 4.08 ERA. He had a strikeout rate of 17.2%, a walk rate of 7.2%, and got ground balls on 50.3% of the balls in play.
Luis Castillo anchors the Mariners rotation as the veteran presence
Seattle’s pitching lineup right now includes Logan Gilbert, George Kirby, Bryan Woo, Bryce Miller, and Luis Castillo. This crew is seen as one of the top rotations in the league. On top of that, the depth features Logan Evans, Emerson Hancock, and Blas Castano, who are still working to make their mark in the Major Leagues. There’s also prospect Jurrangelo Cijntje in the mix, but he’s only had seven starts in Double-A and hasn’t made it to Triple-A yet.
Mariners’ bullpen features eight key arms with limited minor league flexibility
The Mariners’ bullpen is expected to feature Andrés Muñoz, Matt Brash, Jose A. Ferrer, Eduard Bazardo, Gabe Speier, Carlos Vargas, Casey Legumina, and Jackson Kowar.Among these players, only Brash and Ferrer have minor league options available, but both are seen as too important to be demoted.This situation creates some challenges for Criswell, who might be utilized as a long reliever but could encounter roster issues if the team tries to pass him or another reliever through waivers.In the recent move, Jhonathan DÃaz got designated for assignment. At 29 years old, DÃaz played in one Major League game for Seattle in 2025, but he mostly spent his time with Triple-A Tacoma. He pitched 138 2/3 innings there, achieving a 4.15 ERA along with a 19.8% strikeout rate and a 4.1% walk rate. Over five seasons, his Major League career totals 46 1/3 innings with a 4.66 ERA.Also Read: Bob Costas returns to NBC after 39-year legacy to host Sunday Night Baseball pregame show