Paul Sewald was 30 years old and 147 1/3 rough innings into his major-league career when he washed up with the Seattle Mariners. Non-tendered by the New York Mets and toting a 5.50 career ERA, he signed a minor-league deal with Seattle prior to 2021. What his new coaches told him to do ran counter to the entire idea of how he had previously pitched.

“They said when you throw the ball up in the zone, you're very successful,” Sewald said. “That, for me, was, like, an accident up until 2021.”

After initially working on some tweaks in Triple-A, he returned to the majors that May and started dealing. But he was still flinging his fastball just 92 mph, only half a tick faster than with the Mets. He hadn’t added a new pitch; in fact, he cut out his sparsely used changeup and threw just his fastball and slider. Instead, by focusing on keeping the ball up, Sewald was suddenly one of the top five strikeout relievers in the game, with a 39.4 K% wedging him between Aroldis Chapman and Devin Williams.

He earned the Mariners’ trust, rose into a high-leverage role and started logging the occasional save all before he learned the name of the metric that does the most to explain his — and his fastball’s — sudden, prodigious rise. In August 2021, the veteran Sean Doolittle joined Seattle’s bullpen and mentioned a number “way more important than spin rate, induced vertical movement, the whole thing,” as Sewald recalled. It was called Vertical Approach Angle, commonly referred to as VAA.

What VAA measures is easy to understand and visualize if you ever took geometry. Using Statcast data available on every pitch, it estimates the angle at which the ball is traveling when it reaches the front of the plate. Is the ball diving toward the dirt right behind the plate? Or is it still riding almost parallel to the ground when the batter is trying to connect?

All pitches (with the rare exception of some submarine offerings) are moving down, or at a negative angle, when they reach the plate, having started from an elevated mound. Expressed in degrees, one end of the VAA spectrum is “flat,” and the other is “steep.” When you see a particularly sizzling fastball that appears to “rise” and zip over the top of a hitter’s flailing bat, that’s a flat fastball that might be coming in at an angle very close to zero.

Sewald found that he had one of those, maybe the most extreme one in baseball, once he started elevating regularly.

“I kind of looked into it,” he said. “And then I noticed that I was literally at the top of the leaderboard for people who don't throw underhand.”

VAA is just one guiding light in the pitching universe’s ever-expanding array of data, but it’s a particularly good window into how teams, coaches and pitchers talk about their craft now. There’s no one way to achieve success as a pitcher, but there is a burgeoning language being used to describe each pitch’s shape and, in turn, to shape the pitchers who throw them.

Understanding VAA as a pitching metric

Here’s what VAA is not: a simple number that quantifies one thing and tells you what’s good and what’s bad. Alex Chamberlain, who maintains a public VAA leaderboard and has detailed the metric’s implications at FanGraphs, wrote that VAA is useful precisely “because it captures the interaction of multiple pitch attributes at once.”

Those attributes begin with a pitcher’s release point and end with the pitch location. In between, velocity and spin and pitch movement all play a role in determining the ball’s path at the crucial moment when a batter might make contact. You can find breakdowns of each individual component of a pitch, and sharp observers track start-to-start changes to decipher a pitcher’s latest strategies.

Zoomed out, though, there are some broad formulas for success that we can use to explain the language of pitch shape.

Take Minnesota Twins starter Joe Ryan. He’s an example of how the many elements of VAA can work together in a best-case scenario. He throws only 92 mph, but Ryan relentlessly works the top of the zone from a low arm slot, giving the overwhelming majority of his four-seamers an angle hitters rarely see. It’s that combination of factors that VAA captures.

Since the start of 2022, Ryan’s four-seam fastball has run an average VAA of -4 degrees, which puts it among the flattest fastballs thrown by starting pitchers. For a four-seam fastball, -4 degrees is exceptionally flat, while -5 degrees is average and -6 degrees is so steep that every commonly used fastball beyond that threshold is classified as a sinker. (VAA currently offers its most salient lessons in relation to fastballs, but you’ll find even wider variance in the world of breaking balls.)

If the differences between flat, average and steep fastballs seem numerically small, remember how slim the margins are in midair combat with major-league swings. Hitters have fractions of a second to identify what’s coming and take their swings. They are operating on muscle memory, by necessity, and can’t re-engineer their swings to meet each pitcher.

As a result, throwing a fastball that behaves differently than what a hitter has grown to expect — on either extreme — is likely to create an advantage for the pitcher. For flat four-seamers such as Ryan’s, that means whiffs and pop-ups. For a diving sinker or the long-prized downhill four-seamer, it could mean grounders or frozen hitters.

Derek Falvey, the Twins’ president of baseball operations who acquired Ryan in a trade with the Tampa Bay Rays in 2021, said the consideration of vertical angles blossomed as teams advanced beyond countering hitters based purely on their handedness and began thinking about how to attack swing planes.

“How do pitches approach the zone? How do they move? And then you take a step further and say, ‘Well, maybe it's not just about left-right,’” Falvey said. “It's about a certain swing profile with a certain pitch type.”

Ultimately, he said, they’re attempting to describe how a pitch moves when it gets to the plate and how difficult that makes life for the batter. Before VAA was a common acronym in pitching parlance, pitching coach Brent Strom, then with the Houston Astros, used this idea to emphasize the merit of high fastballs in the era of power swings, electrifying Gerrit Cole’s career (among others) in the process.

“I think a young hitter or a 10-year-old can tell you right out of hand if that ball is going to be outside or inside,” Strom said. “It's a little more difficult to tell up and down.”

Today, a focus on verticality defines some of the game’s most thrilling pitchers, and it’s how they define themselves. To wit, Atlanta Braves flamethrower Spencer Strider references his low (read: flat) VAA as a quality he intentionally leaned into.

For visual learners, here are some examples of fastballs that leverage extreme vertical angles to their advantage.

• Flat four-seam (-3 to -4.5 degrees): In addition to Ryan, the Milwaukee Brewers’ Freddy Peralta and aces such as Luis Castillo and Aaron Nola throw very flat fastballs. So does Jacob deGrom — because of course.

• Steep four-seam (-5.5 to -6.2): San Diego Padres starter Joe Musgrove, who stands 6-foot-5, throws a notably steep four-seam.

• Flat sinker (-3.5 to -5.3): This one isn’t very common, but there’s one famous example: Padres closer Josh Hader.

• Steep sinker (-6.2 to -7): New York Yankees closer Clay Holmes and St. Louis Cardinals starter Jordan Montgomery both throw very steep sinkers, which can border on -7 degrees.

If you’re inclined to peruse the leaderboards yourself, Chamberlain’s helpfully offers VAA Above Average, controlling for factors such as pitch type so you can compare pitches without having to memorize league-wide norms. A positive VAA AA means a flatter pitch. A negative number means steeper. And remember: VAA probably tells us the most about the pitches on the extremes.

How pitch shape can help shape pitchers

After years of struggling to unlock a true ace, to generate the strikeouts necessary to dominate major-league hitting in the 2020s, the Minnesota Twins’ pitching staff leads baseball in strikeout percentage and K-BB% early this year. The two biggest reasons — Ryan and offseason trade addition Pablo Lopez — are both deploying modified arsenals that demonstrate a detailed understanding of pitch shape and how it applies to them.

Falvey chuckled when asked to describe the mix of numbers and information used to devise a pitcher’s best path forward.

“There's a lot of ingredients to make that soup,” he said, listing spin, spin axis, vertical movement, horizontal movement and other elements that everyone talks about now. “It's complex.”

In the 2000s, PitchF/X gave the baseball-watching public its first look behind the curtain at what makes good pitches good. In 2015, Statcast added another layer with futuristic-seeming measurements such as spin rate that hinted at answers to mysteries in the realm of “why some 92 mph fastballs are better at missing bats than 99 mph fastballs” and “why some pitchers have fastballs that look and feel heavy.”

Ryan’s four-seam ranks by wOBA as one of the top 10 starter four-seams in baseball since the start of 2022, and you wouldn’t have much of a clue why that is if you went looking at more straightforward measurements such as velocity and spin rate (both unspectacular in Ryan’s case).

Just a few years back, Ryan’s success might’ve remained mysterious. Or it might not have happened this way at all.

See, VAA represents one of the ways baseball’s reams of data and player instruction have meshed successfully. Falvey and the Twins' front office saw Ryan’s eye-popping strikeout totals in the minors, sure. But they were also able to muster a more complete explanation for them and begin to project on his potential.

The pitching lingo today is expansive — there’s also Horizontal Approach Angle (HAA), for the record, which has its own extreme examples in Chris Sale and Nick Lodolo — but it’s fitting. It is rising to the challenge of cataloging a diversifying pitching ecosystem.

“Now that we have all the tools that we can assess that,” Falvey said, “what we do is try and identify players who we think have some ingredients that might — based on the way they throw, where their slot is, what it looks like — maybe there are some differences in the way they approach pitching that we could modify some and make a little better.”

At the most basic level, Ryan’s grand secret is his low arm angle. Throwing from a lower release point — either by being physically shorter or by veering closer to sidearm than over-the-top delivery — is a good starting point for achieving a flat VAA. Ryan stands 6-foot-2, but he releases the ball just 5 feet off the ground — a full 6 inches lower than his 5-foot-10 teammate Sonny Gray, by contrast.

Developed in this era of robust information, Ryan said he first heard the term VAA in 2018, when he visited Cressey Sports Performance, one of the game’s many forward-thinking independent coaching and training facilities. It wasn’t a huge midcareer revelation for him, as it was for Sewald. But the language of reinforcement can also drive reinvention.

For the Mariners’ veteran relief ace, learning about VAA proved that quantitative analysis can spark smart guidance.

“Maybe behind the scenes they knew VAA was my key,” Sewald said of the Mariners’ front office and coaches. “Their biggest balance is trying to figure out, 'What can we tell a player that he can understand vs. what's too much for them to process?' So their idea was throw the ball up in the zone. Very simple, very easy coach-player communication that we've had for years.”

And he bought in — big time. Sewald now seeks out information about the latest research and insight. He touts the benefits of listening to data-derived suggestions to his teammates and proudly brought up a FanGraphs article from 2022 noting how fellow relievers Matt Festa and Penn Murfee made similar strides utilizing VAA.

“I've found the more I've been in the big leagues, the better players talk about baseball more than they talk about other stuff,” Sewald said. “So, like, we spend a lot of time in the 'pen, we spend a lot of time traveling and stuff. There's a lot of VAA talk, there's a lot of, watch a video, let’s talk about that stuff.”

Granted, pitching metrics are unlikely to ever inspire record chases or the thrills of exit velocity. Many stats will remain inscrutable to those outside major-league clubhouses or bespoke training programs. But these numbers are increasingly significant tools for cultivating and appreciating the talents who produce the more conventional kinds of excitement.

“The thing that sometimes frustrates me when I hear people talk about, well, this must be cookie-cutter,” Falvey said. “It's like, no, it's the exact opposite of cookie-cutter. You want to look at each individual player's mix, slot, profile, velocity — you know how it all works — and say, how do we make you the best version of yourself?

“And that's always been the case in the game of baseball. We're just doing it now with some more tools.”