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Mariners bolster bullpen, trading for RHP Gregory Santos from Chicago White Sox

Seattle beefs up their back end for a few mid-level prospects and a pick.

Seattle Mariners v Chicago White Sox Photo by Michael Reaves/Getty Images

The Seattle Mariners have acquired RHP Gregory Santos from the Chicago White Sox in exchange for RHP Prelander Berroa, OF Zach DeLoach, and the 69th overall pick in the 2024 amateur draft, per Jeff Passan of ESPN, echoed by Daniel Kramer of

The trade brings an immediate jolt of life to a Seattle bullpen that had been thinned this winter in multiple trades, with Seattle having dealt Justin Topa, Isaiah Campbell, and Anthony DeSclafani away this winter, as well as relinquishing Paul Sewald, Penn Murfee, and Diego Castillo in the past half a year. The move immediately provides a third high-leverage arm with experience to complement Andrés Muñoz and Matt Brash, and give Gabe Speier a more adaptable role by extension.

The 24-year-old Santos may not be first among the names to know for top tier bullpen arms, given that his breakout first full season (after cups of coffee in 2021 and 2022) came last year for a wretched White Sox club. Used in more mid-leverage outings in the first half of the season, Santos grew into a high-leverage role for a Chicago club that had sparingly few moments that could be described as such. He earned a 3.39/2.65/3.67 ERA/FIP/DRA good for 1.6 fWAR in 66.1 IP across 60 appearances last year. The heavy usage did eventually catch up to Santos, as he was shut down with elbow inflammation late in the year, and as of early December it was unclear as to whether he’d be at full bore yet at spring training’s outset. However, at the moment, the expectation is that Santos should be ready for the start of the season, and the young righty has five more years under contract.

What makes Santos successful is not hard to parse. His average fastball is just shy of 99 mph, and the pitch has the type of arm-side run that would make Usain Bolt envious.

Santos is a two-pitch pitcher, with the heater pairing as one might expect with a firm, low-90s slider. Both pitches can be tweaked for greater sink, and that’s how Santos runs a lofty 53.2% groundball rate thus far, in keeping with similarly lofty numbers in the minors.

Broadly speaking, Santos brings the best of most worlds as a reliever. Though he only struck out 22.8% of his opponents last year, he walked just 5.9%, and when he does let them on he’s capable of tidying up his own messes with groundballs for double plays.

On the way out are a pair of high-minors prospects who Seattle has shown varied levels of faith in, along with a draft pick. Berroa was a 2023 breakout, building on a strong 2022 after coming over to Seattle from the San Francisco Giants in exchange for INF Donovan Walton. His high-90s heat and cutter/slider combo is an elite bat-misser, but Seattle did not have faith in his command to pitch down the stretch in 2023, even as they were forced to the likes of Dominic Leone. Berroa could still be worked as a starter, entering his age-24 season, but will likely get his first taste of Triple-A ball after leapfrogging to Seattle from Arkansas.

DeLoach was a 2020 draftee, with darling characteristics within the front office that bore out inconsistently in game action. Capable of handling all three outfield spots, and showing significant game power, DeLoach has been slowed in his big league trajectory by contact complaints, striking out 27.8% of the time in Triple-A but cracking 23 big flies in 623 plate appearances with Tacoma. The 69th pick in the draft is a nice addition for Chicago, whose high minors depth is grisly, and whose present and future trajectory is extremely difficult to project. If you’re going to trade for a reliever as the Mariners, this is the type of young player to target, who can perform for the organization for years and place even greater pressure on opposing offenses to perform against Seattle’s stellar rotation.