Mariners flesh out bullpen depth, trade for RHP Will Klein from Athletics for international amateur slot money

A little extra heat on the horizon.

The Seattle Mariners announced Tuesday that they have acquired RHP Will Klein in a trade with the Athletics for international slot money. In a corresponding move, they’ve designated recently claimed LHP Tyler Jay for assignment.

Klein had been DFA’d by the Athletics on January 17th to clear a roster spot for newly signed RHP Jose Leclerc. The Eastern Illinois University product was one of three former Panthers to debut in 2024, breaking a 23 year drought of big league representation for the school since former M’s coach Tim Bogar’s final season in the bigs back in 2001. Klein was selected by the Kansas City Royals in the 5th round of the shortened 2020 draft just two picks before Seattle’s selection, RHP Taylor Dollard. He was one-third of the trade return for A’s bullpen ace Lucas Erceg, who featured heavily in Kansas City’s run to the playoffs.

Though he cracked just eight games in the bigs in 2024, Klein’s framework for success is fairly straightforward. This winter, Baseball Prospectus ranked Klein as the 15th prospect in the A’s system, while MLB Pipeline had him 16th and FanGraphs 19th. That’s on the strength of two fastballs, both 95-99 mph typically, clipping into triple digits on some occasions. Similar to recent A’s bullpen arm, and now recent Mariners non-roster invitee Shintaro Fujinami, the heat comes with immense control challenges. Klein has walked between 15-18% of batters he’s faced in the past year, which he does not currently make up for at a pedestrian strikeout rate in the low-20% range. Much of the latter number has to do with an inconsistent ability to demonstrate a threatening off-speed pitch, as Klein’s slider lacks the depth or verve needed to be a bat-misser, particularly given his poor command. You can see it here in a somewhat memorable moment from 2024:

What’s curious is Seattle’s recent efforts to target buy-low bullpen options haven’t matched the type of pitcher they’ve more frequently managed to maximize off the scrap heap in recent years. That may sound like a critique, but it’s primarily an observation and curiosity. While their rotation is flush with highly-drafted fireballers, the M’s have bolstered their competitiveness with standout bullpens. The two best relievers in Seattle’s last half-decade have been Andrés Muñoz and Matt Brash, both known fireballers upon arrival with nasty off-speed. Seattle unlocked the best in Brash, while Muñoz was already seen as a high-leverage arm talent if he could remain healthy. Seattle appears to be seeking new variations of those two, in lieu of maximizing players with less eye-popping velocity but evasive stuff. Since the start of last off-season, acquiring Klein, Fujinami, Carlos Vargas, Mike Baumann, Jackson Kowar, Gregory Santos, and Ryne Stanek has shown a greater interest in maximizing players whose stuff already jumps off the page. That’s in contrast to the Paul Sewald, Collin Snider, Taylor Williams, Drew Steckenrider, Justin Topa, Erik Swanson, Penn Murfee, Austin Voth, Casey Sadler types, with whom Seattle has had more robust success despite none averaging more than 95 mph on their heaters.

Klein’s ability to be optioned to the minors is an obvious bonus for Seattle, who has an atypical number of players out of options in their bullpen. Additionally, as pictured in the header photo, Klein is familiar with his potential Triple-A Tacoma catcher, as Klein threw to Harry Ford in the 2023 MLB Futures Game at T-Mobile Park. The cost of international bonus money is technically trading nothing, since what Seattle has actually traded the A’s is slot space, which is dealt in $250,000 chunks at minimum, and simply allows the A’s to spend additional money on larger signing bonuses for the coming year. In essence, Seattle has given the A’s the permission to spend money, which is amusing in a certain light. DFA-ing Jay to make space is unsurprising, as the southpaw was only recently claimed. Seattle’s been fortuitous this winter, seeing three players successfully pass waivers in the past few weeks and remain in the system, and they may once again with Jay.