Who will be next breakout arm in Seattle's 'pen?

February 18th, 2024

PEORIA, Ariz. -- The Mariners’ success of turning unheralded relievers in Spring Training into legitimate contributors has been one of the club’s greatest success stories of recent memory, which begs to question: Who’s the next Paul Sewald, Justin Topa or Gabe Speier entering 2024?

Manager Scott Servais even coined a nickname for the army of arms that arrived this week -- the “Steckenrider Bucket,” a nod to former Mariners reliever Drew Steckenrider, a non-roster invite in ‘21 who became a key piece to that year’s ‘pen.

The criteria is straightforward: Players with MLB experience elsewhere who have had limited success but possess a plus pitch, or more, that the Mariners believe can unlock more potential.

“Just based on how their career has gone, what the stuff profiles to be, how can they fit on our team? Things like that,” Servais said. “I think we've got four or five of those guys in that bucket.”

Here’s a look at this year’s crop (in alphabetical order):

Previous team(s):
The stuff: 3 mph jump on sinker

Bolton made his MLB debut last year, after five seasons in the Minors, posting a 6.33 ERA with 15 walks in 16 outings. Most of the damage against him was on his four-seam fastball, which opposing hitters had a .378 batting average against. He also throws a two-seamer/sinker, per Brooks Baseball (which tracks Minors data) and saw a notable uptick in velocity. Two-seamers are all the rave in Seattle, so maybe there’s something to work with.

Previous team(s):
Angels, Astros
The stuff: 95th percentile in FB velo in ‘19

The Mariners know him well from his 2019 season with the Angels, when his 1.5 wins above replacement, per FanGraphs, were tied for MLB’s 15th best among relievers. He threw as hard as anyone back then, too, before tumbling out of the organization, leaving baseball all together in ‘21, then pitching in the Minors for Houston from ‘22-23. It’s been a long time since he was elite, but there’s no risk in giving him a look.

Previous team(s):
Royals, Braves
The stuff: 96.9 mph fastball, 32.4% slider whiff rate in ‘23

In 39 outings with the Royals from 2021-23, Kowar had a 9.12 ERA, 49 ERA+ (league average is 100), 2.095 WHIP and a 13.7% walk rate. But the Mariners are bullish on his stuff, which includes a high-90s heater that misses bats and 12-6 slider with some two-plane movement. He also has a changeup in his back pocket that was his best secondary pitch at the University of Florida, where he blossomed into a 2018 first-round Draft pick. And Mariners president of baseball operations Jerry Dipoto is always open to giving former first-rounders a look. Kowar was acquired in the Jarred Kelenic trade with Atlanta.

Previous team(s):
Orioles, Diamondbacks, Rays
The stuff: 4-pitch mix

Krehbiel caught on with the Mariners after being outrighted by the O’s in November and electing free agency. He has 74 innings of MLB experience, most in 2022, when he carried a 3.90 ERA and 100 ERA+ in 56 outings for a Baltimore team that leaned heavily on its bullpen. Last year, his walk rate climbed to 14.2% at Triple-A, where he spent most of the season. He adds intrigue given his diverse arsenal, with a four-seamer, cutter, slider and changeup.

Previous team:
The stuff: 28.2% hard-hit rate in ‘23 (league average was 39.4%)

Claimed off waivers on Feb. 6, Snider has 62 games of MLB experience, over which he’s carried a 5.93 ERA and 72 ERA+, with nearly as many walks (28) as strikeouts (33). But he’s the prototype “Steckenrider Bucket” pitcher given the underlying numbers, which show a potential five-pitch mix. He also kept the ball off barrels last season, with only three homers surrendered, while generating a 52.9% ground-ball rate (league average was 43.1%).

Previous team(s):
Guardians, Diamondbacks
The stuff: 99.4 mph average fastball

Anyone who can touch triple digits will get a look, and Vargas’ heater would’ve been MLB’s seventh-fastest last year if he had enough innings to qualify for leaderboards. His problem has been harnessing it, evidenced by an 11.9% walk rate over four Minors seasons and an 18.2% clip in five outings with the D-backs last year. Acquired in the Eugenio Suárez trade, Vargas should see action in the Majors this season, even if he doesn’t win one of the 1-2 available bullpen spots this spring.