The Mariners have optioned right-hander Gregory Santos to Triple-A Tacoma and recalled fellow right-handed reliever Will Klein in his place, per a team announcement.
It’s the first time in nearly three years that Santos has been optioned to the minors. He was a notable trade acquisition in the 2023-24 offseason, with the Mariners sending prospects Prelander Berroa, Zach DeLoach and a Competitive Balance (Round B) draft selection to the White Sox in return.
At the time of the swap, Santos was fresh off an excellent breakout season in Chicago and had five years of club control remaining. His 2023 campaign with the South Siders featured 66 1/3 innings of 3.39 ERA ball. Santos had averaged 98.9 mph on his sinker while turning in strikeout, walk and ground-ball rates of 22.8%, 5.9% and 52.5%, respectively. He’d started that season in a low-leverage role but found himself pitching more meaningful innings as the year went on; he finished with five saves and six holds. It looked like the start of a lengthy run as a quality high-leverage reliever.
As we see all too often with pitchers, however, injuries intervened. Santos was diagnosed with a lat strain last spring and spent the first three-plus months of the season on the injured list as a result. He returned in early July but was back on the 15-day IL less than a month later, this time owing to biceps inflammation. He returned in the season’s final week and pitched a pair of scoreless innings.
Heading into 2025, Santos looked to be on track for a rebound. The lat strain was behind him, he’d finished the prior season healthy, and he posted a 1.59 ERA in six spring appearances (one run in 5 2/3 innings). That hasn’t played out whatsoever.
Santos’ once premium command has been nowhere to be found. He’s pitched seven innings and faced 36 batters. Eight of them have reached via base on balls (albeit, two of them being intentional). He’s also tossed a pair of wild pitches. Equally or more concerning is the fact that he hasn’t recorded a single strikeout yet. He’s still getting heaps of ground-balls (63%), but he’s missing badly and not inducing chases off the plate. His 11.5% opponents’ chase rate is the fourth-worst among all pitchers with at least five innings this year. His 4.6% swinging-strike rate is tied for ninth-worst.
There hasn’t been a major drop-off in Santos’ velocity. His sinker is down a bit, sitting at 98 mph, but that’s less than a one-mile gap from his 2023 peak. He’s had a bit more of a pronounced drop in his slider velo, but there’s no reason to believe he’s injured at the moment. (He is, after all, being optioned and not placed on the 15-day IL.) Santos has seen some changes in his release point from 2023 to 2025, but again, it’s not necessarily a drastic difference. For now, he’ll head to Triple-A Tacoma for a reset and look to get back on track.
It’s possible, though not yet certain, that today’s demotion could alter Santos’ path to arbitration and to free agency. He entered the season with two years and 55 days (2.055) of big league service, meaning he needed 117 days on the roster to reach three years and keep pace for arbitration eligibility this winter and free agency following the 2028 season. Of course, those factors will be rendered moot if he can’t get back on track and reestablish himself as a credible big league reliever.
Klein has actually had similar struggles to those of Santos down in Tacoma this year. He’s faced 36 batters and walked seven of them while plunking another and being charged with four wild pitches. He’s at least missing bats however and is doing so at an eye-popping rate; Klein has fanned 36.1% of his opponents and is sitting on a strong 13.8% swinging-strike rate. He’ll give Seattle a fresh arm one day after four relievers (Santos among them) needed to cover 3 2/3 innings following a rough start from Luis Castillo.