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In recent years, the Mariners have developed a bit of a reputation as a major pitching lab. Not just through their minor league system, but also the success stories of journeyman relievers coming through Seattle and turning middling careers into All-Star/Team USA appearances. A part of that is that the Mariners have a very specific pitching philosophy and pitching profile they look for. Josh Simpson fits the profile and philosophy.
[Editorial note: The 40 in 40 series was scheduled to a triumphant, thematic close yesterday with the potential Opening Day battery of Bryan Woo and Cal Raleigh. Then accounting informed us we had overlooked one later-off-season acquisition. Management sincerely regrets the error. Please pretend this story ran early last week. And go back and read all the 40 in 40s you might have missed. Errrrm. 40 in 41.]
Rule 1: You gotta throw a slider and sinker
When I started writing this 40 in 40, I really expected to find a slight trend, but I’m not exaggerating when I say that to play in the Mariners bullpen, you have to throw a slider and expect to throw it all the time:
- Matt Brash Slider usage: 61%
- Andrés Muñoz Slider usage: 50%
- Eduard Bazardo Slider usage: 43%
- Gabe Speier Slider usage: 26%
- Carlos Vargas Slider usage: 19%
- Josh Simpson Slider Usage: 6%
I don’t think it’s a coincidence that the Mariners continue to use and acquire guys with high-end sliders with a lot of movement, and then help them to refine it into one of the most dangerous pitches in the league. More to the point, the Mariners were ranked 6th in terms of slider usage by pitchers in 2025. As a team, they threw the slider 26% of the time.
Now the Mariners are smart enough to know that most pitchers are not Mariano Rivera and can’t rely on one pitch most of the time. Which is why you also need to be able to throw a sinker if you wanna join the Mariners arm barn, and expect to throw it right alongside your slider:
- Carlos Vargas Sinker usage: 63%
- Eduard Bazardo Sinker usage: 41%
- Gabe Spier Sinker usage: 30%
- Josh Simpson Sinker Usage: 22%
- Matt Brash Sinker usage: 22%
- Andrés Muñoz Sinker Usage: 12%
As a team, the Mariners threw a sinker or sinker-like pitch 23% of the time, good enough for second in MLB overall.
While Simpson isn’t exactly a major slider pitcher, he does throw a sweeper more than any other pitch. At a time when the sweeper is still riding the back end of a crest in popularity, the Mariners have tempered their adoption of the pitch, throwing just 5.8% sweepers in 2025 (19th-most in MLB), down from 7.1% (14th) in 2024, 6.9% (12th) in 2023, and 7.2% (7th) in 2022 per Baseball Savant. Simpson is already a pretty heavy sinker thrower, but he favors his sweeper over his slider most of the time. With the Marlins, the sweeper was his most effective offering, generating whiffs over 40% of the time, but his infrequently-used slider had a distinct shape and could be effective as well.
That only tells some of the story for Simpson’s sweeper, however, as he only really uses it in lefty-lefty situations, rarely throws it to righties, if at all. Now, as a left-hander, it may be that he doesn’t pitch to many righties, but throwing the pitch to righties only 11% of the time suggests to me it’s a conscious choice rather than a lack of opportunity. Right now, Simpson goes to the sweeper and the curve most often overall, but I think the numbers are there to find success with a more slider-sinker combo. The slider and sinker are much closer in speed which makes tunneling pitches more effective. Plus, as told to me by John Trupin, the wrist motion for the sweeper and slider is very similar, the difference between throwing a frisbee and flicking a light switch. While it’s obviously not a one-to-one, I feel there’s potential for Simpson to fully embrace the Mariners’ pitching philosophy and succeed.
Rule 2: You gotta attack the zone
The Mariners have made no secret about keeping their pitchers in the zone and not being afraid to attack hitters directly. The Mariners were third in the league for pitches thrown inside the zone at just about 54%.Bryan Woo was second among all pitchers at 57% of pitches being in the zone. Clearly, this is a strategy the Mariners have fully embraced, and something the pitchers they bring in need to be able to do without fear. In 30 innings, Simpson had a zone percentage of 54%. Despite this, Simpson ran an atrocious 6.46 BB/9, the 3rd-highest in MLB among 475 pitchers with at least 30 innings in 2025. He’s the only pitcher in the top 150 of Zone% to manage such a poor walk rate (and really nobody else is close).
Clearly, Simpson is willing to go at a batter, and willing to do it at a rate the Mariners are happy with. He was, in some ways, astoundingly unsuccessful in this approach a year ago. There’s a reason the Columbia product (the school, not the country) only managed 30 innings for the Marlins last year, but with such an outlier on the outcome end Seattle may see this as a puzzle they can solve I’m hoping that, with some adjustments from the Mariners’ pitching lab, we could see a whole new player this season.
Rule 3: Be a part of at least one transaction
The Mariners have been very active on the waiver wire, trade market, and DFA postings to build out the bullpen they have now. None of the relief pitchers on the Mariners 2025 roster were originally drafted by Seattle, and only Brash made his big league debut with the Mariners. Not to be rude, but the Mariners take a real “one man’s trash is another man’s treasure” type perspective to the bullpen, and to their credit, it has worked out for the most part. Simpson definitely falls within that category. Simpson was acquired from Miami for cash considerations in early February. I don’t know what it is, but the Mariners seem able to give guys on their second (or last) chance the spark to keep things going for a while longer or step up in a way they never have before. Gabe Speier was just a face in the crowd in Kansas City, Baltimore traded Eduard Bazardo for a low-minors reliever, Carlos Vargas was a toss-in prospect from the original trade of Eugenio Suárez to Arizona, Matt Brash was a player-to-be-named-later, Muñoz was a talented but unreliable and majorly injured prospect with the Padres.
It’s the engine that’s fueled much of Seattle’s success in the 2020s, fueled by bullpen body after bullpen body. Hm? What’s that? What happens after the Mariners are done with you? Don’t worry about all that; we’ll cross that bridge when we get there, or you’ll cross it not, so much for the rest of us. While Simpson has a questionable track record from his time in Miami, the variety of interesting secondaries and ability to get groundballs while pitching in the zone fits what the Mariners are looking for, and he’ll likely have the chance to tweak things in Tacoma before his big league return sometime this summer in Seattle.