40 in 40: Paul Sewald is outwitting, outplaying, outlasting

The old saying in academia for professors just starting out in their careers is “publish or perish”—meaning, in addition to teaching and research duties, one has to constantly produce material demonstrating relevant importance to the scholarly community to justify a position in the hyper-competitive world of academia. The world of being an MLB reliever is similarly defined by “what have you done for me lately”, with relievers constantly needing to adapt to trends that dominate MLB in a limited sample size; punchouts or perish. For relievers who aren’t blessed with a cannon of an arm that can casually hurl triple digits like your grandma firing off holiday delights from a cookie press, that requires attention to the physics of what makes baseballs hard to hit and a PhD where the D stands for “deception.” It also requires understanding when batters are wise to your wily tricks, and the flexibility and creativity to adjust, evolve, and survive.

By now, the secret of Paul Sewald is well-known around baseball, including his journey from 2021 Tacoma Opening Day starter to dominant reliever and de facto closer for the big-league club. It’s a feel-good story, the kind that’s easy for fans to love: long-suffering player for a team that’s not maximizing his skills gets fresh start and has a later-career breakout. It’s an even feelier-gooder story because Sewald is one of the best humans in the game: a considerate teammate who is generous with his time, deeply involved in charity work and committed to creating better outcomes for everyone, with just enough of a fiery, competitive edge to keep him from being a saccharine goody-goody. (Not that there’s anything wrong with that. We love a squashy marshmallow around here. But we love Sewald Screams even more.)

This year, the tweak Sewald made to stay one lesson ahead of the league was on his slider. In 2022, Sewald threw his slider even more, almost a 50-50 split with his fastball rather than the 60-40 split of 2021. Sewald’s slider is an outlier, with significantly less drop than the average MLB slider, but the thing the Mariners have emphasized with Sewald is worrying less about two-plane movement and focusing on maximizing sweep (horizontal movement) on the slider. In 2022, the slider swept just a little bit less on average, but still tempted batters to whiff about 40% of the time. In Eno Sarris’s roundup of the top ten pitches in baseball purely by Stuff+, which measures only the physical characteristics of pitches, Sewald’s slider comes in at #5.

While the slider doesn’t generate a ton of swings—batters swing at it only about 42% of the time—when they do swing, they either whiff at it or foul it away. In 2022, Sewald suppressed batters to a wOBA of just .204 on the pitch, and xSLG suggests he even got a little unlucky on the pitch—an xSLG of .277 vs. the .304 actual slugging percentage. That’s even better (weaker) contact than he got off the pitch in 2021, even if he’s not generating as many whiffs on it with a similar number of swings.

But living on a slider is tricky. If batters don’t offer at it, it’s difficult to get Sewald’s slider called for a strike because of its movement characteristics, and while it’s a difficult pitch for righties to handle—the intense glove-side sweep away causes a lot of ugly swings—if it doesn’t wind up properly backfooted on a lefty batter, it can wind up in that lefty loop zone. Similarly, a righty who is sitting slider can ambush the pitch and time their swing up to contact the ball before it breaks away from the hitter, as Marcus Semien does here in a 2-1 count:

In 2021, what made Sewald so effective was his ability to pair his slider with his fastball, a high-whiff pitch that served as his putaway pitch. What’s impressive about Sewald’s fastball is it succeeds despite below-average velocity due to other characteristics of the pitch, primarily his Vertical Approach Angle (VAA). VAA is the angle at which a pitch crosses the plate, where the larger the negative number, the steeper the “drop” on the pitch. As the ball travels from the pitcher’s hand (release point)—which remember, is already on a downward slope because of the pitcher’s mound—it will continue to be subject to the forces of gravity, so there’s really no such thing as a “rising” fastball, as all pitches are subject to these forces. However, some pitchers have a more shallow VAA than others; among pitchers who threw more that 400 four-seam fastballs last year, Sewald has the shallowest VAA, at -3.5°. Despite throwing his average fastball well below MLB average—in the 35th percentile—Sewald is able to generate above-average swings and misses on the pitch due to its deception.

In 2022, however, Sewald’s fastball was less toothsome for batters, who again offered at the pitch 55% of the time but whiffed at it just under 30% of the time, while fouling it away another 42% of the time—still good numbers, but not as dominant as 2021, when batters offered at the pitch about the same amount but whiffed more like 33% of the time, good for third-highest in baseball on a four-seamer. That’s a small but significant difference. In 2021, Sewald ranked 23rd among qualified relievers (those who threw 100+ fastballs) in whiffs/swing; in 2022, he was down to 50th. His overall chase rate dropped from the 70th percentile in the league to the bottom 13th percentile.

It was never likely Sewald would recapture his mega-strikeout form in 2022; with the league having an entire season’s worth of data on him, the surprise factor was largely gone. But Sewald, ever adaptive, was already focused on a different, more sustainable goal: creating weak contact when batters do swing. What Sewald lost in strikeouts he made up for in limiting hard contact, ranking in the 90th percentile for expected batting average and average exit velocity, while improving his rate on hard hit balls from the 36th percentile to the 82nd. It won’t make highlight reels, but Sewald getting an inning-ending groundout from Jeremy Peña to end the 12th inning of ALDS Game 3 is as important as any out he made this season.

The next adaptation Sewald will have to make, though, is guarding against the longball. Occasionally a lefty will loop the slider—Ohtani, particularly, loves golfing a pitch over the fence that comes in at his shoelaces—or a savvy righty will figure out how to ambush it. But with Sewald’s pitch characteristics on the fastball, if he misses his location, it winds up over the fence, like this heartbreaking go-ahead homer to Manuel Margot back in May:

It’s a tough ask for any player to be perfect, but because of the nature of Sewald’s role as a back-end reliever and the characteristics of his fastball, he basically needs to be perfect with his location. Batters are still swinging at his fastball but missing it less, so it’s imperative he limit mistakes to homers like this fluky Rafael Devers one from June, which had an xBA of just .530, and less like the Margot one above.

What’s helpful for Sewald is because batters are swinging at the fastball more but fouling it away, he’s able to get into favorable counts quickly; even with a waver in command in 2022, out of 242 plate appearances, he was only in a full count in 38 of those. He started out with a first pitch strike over 60% of the time, just slightly above MLB average, but from there was quick to move batters into two strike counts. That’s key for Sewald because the less he is behind in counts, the more he’s able to keep batters guessing as to whether they’ll see his fastball or slider:

Baseball Savant

Pitching from behind = having to throw the fastball = narrower band of success. Narrow bands of success are admittedly kind of Sewald’s thing, but what’s helpful is now with the emergence of Matt Brash and Andrés Muñoz, the Miser Brothers of the Mariners’ bullpen, Sewald can ideally be deployed as part of a three-headed backend bullpen monster and not have to carry the closer’s mantle by himself. But should the youngsters struggle, the ever-adapting Sewald is there as a steady veteran presence, still rewriting the book on his MLB career.