Mariners Acquire Cooper Criswell

The Mariners announced that they have acquired right-hander Cooper Criswell from the Mets in exchange for cash considerations. He was designated for assignment this week when New York acquired Freddy Peralta and Tobias Myers from the Brewers. Left-hander Jhonathan Díaz has been designated for assignment by Seattle as a corresponding move for Criswell. Jorge Castillo of ESPN first reported that the Mariners would be acquiring Criswell. Ryan Divish of The Seattle Times reported the cash going the other way.

Criswell, 29, has the reputation of a serviceable swingman or back-end starter. His most extensive big league look came in 2024 with the Red Sox. He tossed 99 1/3 innings for Boston that year over 18 starts and eight relief appearances, allowing 4.08 earned runs per nine. His 17.2% strikeout rate wasn’t especially high but he limited walks to a 7.2% pace and induced grounders on 50.3% of balls in play.

Despite that solid season, he got pushed down the depth chart in 2025. The Sox acquired Garrett Crochet, signed Walker Buehler and got Lucas Giolito back from his injury absence. Criswell only made seven big league appearances last year. He spent most of the year in Triple-A, where he tossed 65 2/3 innings with a 3.70 ERA, 24.5% strikeout rate, 10.1% walk rate and 49.4% ground ball rate.

He exhausted his final option in 2025, pushing him to a fringe roster position. He and the Sox agreed to a deal in November, guaranteeing him $800K in 2026, even though he had not yet qualified for arbitration. That salary is only marginally above the $780K minimum in 2026.

The hope with a deal like that it would disincentivize other clubs from claiming him via waivers. It would also make Criswell less likely to elect free agency after clearing. He has a previous career outright and therefore has the right to reject further outright assignments in favor of the open market. But since he has less than five years of big league service time, he would have to walk away from the money in exercising that right.

That hasn’t gone as planned. The Sox designated Criswell for assignment in December but the Mets claimed him off waivers. As mentioned, the Mets bumped him off the roster this week. If they had any hope of passing him through waivers, the Mariners presumably called and told them it wouldn’t happen.

Seattle has a strong rotation but the depth isn’t amazing. The front five of Logan Gilbert, George Kirby, Bryan Woo, Bryce Miller and Luis Castillo is one of the best in the game. But beyond that group are guys like Logan Evans, Emerson Hancock and Blas Castano who haven’t yet proven themselves to be effective big leaguers. Switch-pitching prospect Jurrangelo Cijntje is on the way but he has only seven Double-A starts under his belt and hasn’t reached Triple-A yet.

Criswell gives the M’s a useful guy to add to the mix, though the roster fit is a bit tight at the moment. As mentioned, the club already has five good starters. Criswell could be in the bullpen as a long reliever but the relief group is also crowded. The Mariners currently project for an eight-man bullpen consisting of Andrés Muñoz, Matt Brash, Jose A. Ferrer, Eduard Bazardo, Gabe Speier, Carlos Vargas, Casey Legumina and Jackson Kowar. No one in that group can be optioned to the minors except for Brash or Ferrer and they’re too good to be sent down. Perhaps the M’s will try to pass Criswell, or someone else in that group, through waivers at some point for extra flexibility.

As for Díaz, the 29-year-old began today in the rotation depth group alongside Evans, Hancock and Castano but the Mariners evidently prefer Criswell to Díaz in that mix. Some websites list Díaz as still having a minor league option but he was optioned for extended stretches throughout the 2022, 2024 and 2025 seasons. Teams are sometimes granted a fourth option on a player but only if they don’t have five “full” professional seasons, where a “full” season is defined as 90 active days. Díaz first reached full season ball way back in 2017 and has been fairly active since then, so he shouldn’t qualify for a fourth option.

His major league track record is still fairly short. He has appeared in five big league seasons but with just 46 1/3 total innings pitched across those. He has a 4.66 ERA, 15.1% strikeout rate, 12.3% walk rate and 45.2% ground ball rate. He only made one big league appearance last year, spending the rest of the season on optional assignment with Triple-A Tacoma in the hitter-friendly Pacific Coast League. He gave that club 138 2/3 innings with a 4.15 ERA, 19.8% strikeout rate, 4.1% walk rate and 46.9% ground ball rate.

The lefty will be in DFA limbo for a week at most. The waiver process takes 48 hours, so the Mariners could field trade interest for as long as five days. He has a previous career outright and would therefore have the right to elect free agency if he were to clear waivers.

Photo courtesy of Eric Canha, Imagn Images