Mariners trade for reliever Santos from White Sox

February 3rd, 2024

SEATTLE -- Seeking to replace a high-leverage presence in their bullpen, preferably with an arm possessing plus-plus stuff, the Mariners swung a trade with the White Sox on Saturday for reliever to accomplish just that.

Mariners receive: RHP Gregory Santos
White Sox receive: RHP Prelander Berroa (Mariners’ No. 15 prospect), OF Zach DeLoach (No. 25 prospect), No. 69 overall pick in 2024 Draft

Seattle parted with two prospects that were slated to contribute in the Majors this season, along with its selection in Competitive Balance Round B of this year’s MLB Draft, one of the few picks across the league eligible to be traded.

Santos should slot into a role comparable to the one held by Justin Topa, who was the key piece in Seattle's trade with Minnesota on Monday that netted the Mariners former All-Star second baseman Jorge Polanco. Topa’s departure, along with Paul Sewald’s at last year’s Trade Deadline, opened the door for closer duties to a hybrid of Andrés Muñoz and Matt Brash, but they also created voids within a bullpen that has been one of the American League’s best the past three seasons.

Santos, 24, made 60 appearances for the White Sox last season and was injected into many of their highest-leverage pockets after All-Star closer Liam Hendriks underwent season-ending Tommy John surgery in June. He carried a 3.39 ERA (132 ERA+, where league average is 100) with a 22.8% strikeout rate, a 5.9% walk rate and a 1.296 WHIP across 66 1/3 innings.

Yet the underlying metrics paint the picture of a pitcher with even more potential, and he’ll now join an organization with a track record for exploiting the very best strengths of its arms.

Santos’ best pitch is a slider that sat at 91.9 mph last season and generated a 37.5% whiff rate, per Statcast, holding hitters to a .196 batting average and a .203 slugging percentage. He pairs it with a sinker/two-seamer that averaged 98.9 mph and consistently reached over 100 mph, having made the shift from a four-seam fastball.

Santos’ season ended in late September when he hit the injured list with right elbow inflammation. White Sox general manager Chris Getz told’s Scott Merkin at the Winter Meetings that Santos had just begun an offseason throwing program, which could delay his start to Spring Training. The Mariners plan for him to have six to eight Cactus League outings, then be ready to go, a source said.

Signed by the Red Sox out of the Dominican Republic in 2015, Santos was traded to the Giants in '17 and spent two seasons in San Francisco (2021-22) but with only five appearances. He took off in ‘23 after being traded to the White Sox the offseason prior. Santos won’t be eligible for arbitration until ‘26 and free agency until ‘29.

He’ll now have an even bigger opportunity in Seattle for a team expecting to contend, and with its bullpen part of its blueprint for success. Though Santos saw leverage situations regularly in 2023, he was doing so for a 101-loss team that was out of the postseason picture well before October.

As for what the Mariners dealt away, Berroa, 23, possessed comparable stuff to Santos, but he’s struggled mightily to harness it. After debuting on July 21, Berroa walked three of the eight batters he faced in the Majors, which clouded some trust in leverage moments from Mariners manager Scott Servais. He also had a 14.1% walk rate at Double-A Arkansas, slightly better than his 16.8% clip the year prior but still high. Some have pointed to his command being a focus issue rather than stuff, but he’ll nonetheless need to be in the zone more to be a consistent big league contributor.

DeLoach, 25, was Seattle’s second-round pick in the shortened 2020 Draft but has yet to make his MLB debut, though that was likely to come this season after he was added to the 40-man roster in November. The former Texas A&M Aggie slashed .286/.387/.481 (.868 OPS) with 23 homers and 88 RBIs over 138 games last season, all at Triple-A Tacoma. But he also carried a 27.8% K rate that left some scouts pondering how he’d handle Major League pitching.

As for the Draft pick, it’s the first that the Mariners have traded under president of baseball operations Jerry Dipoto and general manager Justin Hollander. The two have been leery of dealing such picks, underscoring the value they see in Santos.