The craft of pitching changed before our eyes in 2017, largely out of necessity.

That was the year baseball was taken over by the viral spread of the “flyball revolution,” the growing movement of hitters armed with launch-angle data and rebuilt, uppercut swings seeking to lift the ball at all costs. What started with a handful of devotees several years ago had become a wave by last season, as hitters leaguewide smashed the record for home runs, with 6,105 — an increase of 45.8 percent over 2014’s 20-year low.

In the age-old battle of adjustments between pitchers and hitters — the fundamental matchup upon which the game is based — the former group, which holds the distinct advantage of initiating the action, was faced with an unprecedented and existential threat from the latter.

It is a threat that is expected to intensify as the 2018 season approaches, with anecdotal evidence of even more hitters becoming launch-angle disciples this past offseason, and the ongoing, collective response from pitchers will be one of the most fascinating subplots of the new season.

“You’re already seeing a big shift,” Tampa Bay Rays third base coach Matt Quatraro, who spent the past four years as the Cleveland Indians’ assistant hitting coach, said in mid-March. “You could see pitchers changing the way they pitched last year, but now this spring it’s definitely becoming more prevalent.”

That shift in pitching theory can be summed up like this: fewer sinkers, fewer low pitches, more breaking balls, more four-seam fastballs, more high pitches. The logic, while an oversimplification, goes like this: If hitters, with their uppercut swings, have figured out how to go down and scoop low fastballs — the pitcher’s bread and butter for generations — over the walls, they would have a much tougher time doing so with high fastballs and well-placed breaking balls.

“It’s a constant cat-and-mouse cycle of hitters adapting and pitchers adapting,” said Washington Nationals pitching coach Derek Lilliquist, who pitched in the majors from 1989 to 1996. “In my era of pitching, there were [a] ton of [hitters] who handled fastballs at the belt and above. Those were the home runs in that era. You had to keep the ball on the knees. But now it’s shifting.”

A new approach to pitching

While much was made about the shift in teams’ pitcher-usage patterns in 2017 — with data-driven front offices and managers more reliant than ever on relievers, who pitched a record-high 38.1 percent of all innings, and less likely to allow starters to face a lineup for a third time in a game — the steady shift in the way pitchers collectively approached hitters was less noticeable, but perhaps even more revealing.

You could watch the trend play out month-to-month in the data from 2017. Here are the percentage of overall pitches leaguewide that were sinkers, month by month, according to FanGraphs: April, 19.6 percent; May, 19.0; June, 19.2; July, 18.4; August, 18.4; September/October, 16.9. That comes out to a 16 percent decline across just one season, and it continued a four-year decline in the prevalence of sinkers, from 21.5 percent of all pitches in 2014, to 20.4 percent in 2015, to 18.7 in 2016 and down to 18.6 in 2017.

The difference was made up mostly by breaking balls, as curveballs and sliders accounted for 23.2 percent of all pitches in 2014, 23.6 percent in 2015, 24.6 percent in 2016 and 27.1 percent in 2017 — a four-year climb of 16.8 percent.

The five teams that threw the most curveballs (defined by Statcast as curves plus knuckle-curves) in 2017 — the Cleveland Indians, Boston Red Sox, Los Angeles Dodgers, Houston Astros and Chicago Cubs — were all division winners, and most are considered among the most analytics-driven organizations. That was almost certainly more than coincidental.

“It’s my best pitch,” said Astros right-hander Lance McCullers, who famously threw 41 curveballs in a 54-pitch relief outing against a fearsome New York Yankees lineup in Game 7 of the American League Championship Series, including 24 straight at one point. “If hitters are going to be up there throwing Hail Marys with every swing, you have to run with what you’re good at.”

But it wasn’t only pitch selection that was changing, but also pitch placement. Here, using data from Statcast, are the month-to-month averages of pitches characterized as high in 2017: April, 27.1 percent; May, 28.8; June, 32.2; July, 33.1; August, 33.9; September/October, 33.0. (The major league leader, among pitchers who threw at least 300 pitches in 2017, was Nationals closer Sean Doolittle, with 60.8 percent of his pitches considered high.)

A generation ago, the typical ace pitcher was a sinker-cutter-slider guy who came up hearing “keep the ball down” from every pitching coach from Little League to the majors.

“As a kid, you’re taught, ‘Down in the zone, down in the zone,’ ” said San Francisco Giants catcher Buster Posey, who was also a star pitcher as an amateur. “And when I first got up [to the majors], you were still seeing tons of [sinkers] and hard sliders. But now, hitters are geared to handling hard velocity down in the zone and hard sliders, so what you’re seeing is elevated four-seamers and curveballs making more of a comeback. It’s definitely something we’ve talked about this spring.”

The launch-angle movement began, in a sense, as a counter-weapon to the prevalence of great sinker pitchers, teaching hitters who would normally pound those sinkers into the ground to get under them and drive them to — and over — the wall. As the movement has spread, the average launch angle of batted balls in the majors has risen from 10.1 degrees in 2015 to 10.8 degrees in 2016 and to 11.1 degrees in 2017.

Faced with opposing lineups full of would-be home run hitters — in an unprecedented, homer-happy environment in which a record-setting 41 hitters smashed 30 or more last year — pitchers are left with a choice: adapt or perish.

“I think we’re still figuring out how to approach” pitching to lineups full of flyball-minded hitters, said Oakland Athletics Manager Bob Melvin, a former catcher who played 10 years in the majors.

“It used to always be, if you kept the ball down you’d have a better chance of keeping [a batted ball] on the ground. But now you have guys who can lift that ball. I’m not sure anybody has figured out how to combat that fully on the pitching side.”

Old habits die hard

Before the rise of the launch-angle movement, the standard four-seam fastball — generally thrown the fastest of any pitch, with a rising movement (or at least that perception) through the hitting zone — while still the dominant pitch in the game, was slowly falling out of favor, reaching a low of 34.8 percent of all pitches (according to FanGraphs) in 2012. But its use has climbed back since then, hitting 37.2 percent in 2016 before falling slightly to 36.7 last season.

Some believe the shift in pitch-usage is tied into another apparent shift in the way umpires are calling the strike zone.

“Three years ago, umpires would give strikes off that outside corner but not necessarily up [in the strike zone],” said Tampa Bay’s Quatraro. “But now, they’ve brought the ball onto the plate and have [moved the strike zone] up and down more. Add into it the fact there are so many guys who throw so hard, and there are now fewer guys who finesse the corners. So more guys are now going to work the top and the bottom of the zone.”

But as teams work to change pitchers’ mentalities, convincing them they can be effective pitching up in the strike zone, they are bumping up against the entrenched, keep-it-down approach that has been preached for generations. When pitchers are taught all their lives to stay low in the strike zone, convincing them they can be effective with high fastballs takes the proper touch.

“It’s a challenge,” Posey said. “When you’ve been taught one way all your life, changing that is a tough transition.”

Part of the challenge is in getting players to understand what the data shows, but another part is avoiding the tendency to apply one approach to everyone — in other words, identifying which pitchers can survive a shift in approach and which can’t.

“It’s still dangerous throwing the ball up in the zone. That hasn’t changed,” said Colorado Rockies Manager Bud Black, a former pitcher. “You have to throw it at the right height. If you throw it too high they’ll take it [for a ball], but if you miss it low, they’ll crush it. It isn’t for everybody. There are pitchers whose style and stuff allows them to pitch up there, guys we identify as highball pitchers, and we encourage them.”

The sinker hasn’t gone away, nor is it ever likely to. There remain great pitchers who rely on it for more than half of all their pitches, and some — such as left-handed reliever Scott Alexander (93.4 percent of all his pitches) and Nationals right-handed reliever Brandon Kintzler (81.7 percent) who were effective in 2017 while using almost exclusively sinkers.

When Lilliquist, the Nationals’ pitching coach, was asked if the launch-angle movement could ever make the sinker obsolete, he looked offended.

“Absolutely not,” he said. “Movement is always going to play. It’s not just keeping the ball down — it’s also the movement that’s key. Guys like [Tanner] Roark and Kintzler — they’re still going to go with their strengths. The [hitters’] swing path has definitely changed. But there’s still room [for a pitcher to be effective] from the knees down, and there’s still room from the belt above. . . . It’s more of a dual message now: Get the ball at the knees or below, or at the top of the strike zone and above. Stay out of the mid-thigh.”

Even if individual pitchers are going to stick with what has always worked for them, the evidence of a defined, leaguewide shift — away from sinkers and low strikes, and toward four-seamers, curveballs and high strikes — is visible in the numbers.

It remains the timeless and fundamental atom of baseball’s essence: the hitter vs. the pitcher. When the hitter adapts, the pitcher must adapt as well, and vice versa. The direction the game moves in 2018 — with hitters continuing to launch the ball out of the yard in record numbers, or pitchers gaining back some ground — could depend largely on which group does it better.

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