MLB’s Endangered Species: Pitchers Who Pound the Strike Zone

On Tuesday night in Arizona, Diamondbacks southpaw Patrick Corbin pitched the best game of his career and made the second-best start of the 2018 MLB season so far. In a 1-0 win over the Giants, he recorded his first career shutout, walked one, whiffed eight, and allowed only one hit, a check-swing single against the shift with two outs in the eighth inning.

Corbin is the biggest reason for the first-place Diamondbacks’ 12-5 start. The 28-year-old lefty has been brilliant through his first four outings, striking out 37 batters, walking five, and allowing only five runs in 27 1/3 innings. Knowing nothing else but his superb walk rate and his ability to go deep into games, one might surmise that Corbin has been pounding the strike zone more than in years past and pitching more economically on a per-batter basis. In fact, the opposite is the case: Corbin has thrown a career-high 3.80 pitches per plate appearance this season, well above his pre-2018 average of 3.60. Among qualified National League starters, only one, reigning Cy Young Award winner Max Scherzer, has amassed more wins above replacement than Corbin. Yet it’s also true that no qualified NL starter has thrown a lower percentage of pitches in the strike zone. Corbin is in the zone because he’s staying out of the zone.

Corbin is among the most successful pitchers who’ve adopted the tactic that FanGraphs’ Jeff Sullivan calls “McCullersing,” after the Astros’ Lance McCullers, who uses his breaking ball (in his case, a curveball) as his primary pitch despite the sport’s age-old insistence that the fastball come first. (In Game 7 of last year’s ALCS, McCullers threw 41 curves in 54 pitches as the Astros collectively hurled the highest single-game percentage of curveballs on record.) As Sullivan noted earlier this month, Corbin’s slider has long been by far his best pitch, placing in the 79th percentile from 2012 to 2017 in FanGraphs’ pitch-type run values (on a rate basis), compared to the ninth percentile for his fastball and the first percentile for his changeup. Given that discrepancy, it was only logical for Corbin to ramp up his slider usage, which he started doing last summer, and vary the speed of the pitch the way that McCullers and Rich Hill, another breaking-ball trailblazer, do with their curves.

“His slider was always good,” Diamondbacks pitching strategist Dan Haren says. “We wanted to make it 50-50 fastball-slider. He started throwing the slow one just to dump in for strikes and the harder one for put-away. I think around June of last year this happened. [We] also made some simple adjustments with certain pitch selections in specific counts.”

As a result of the team’s tweaks to Corbin’s approach, his slider rate has spiked, and his zone rate and O-Contact rate—the percentage of swings outside the strike zone on which hitters make contact—have plummeted.

Although the game’s average fastball speed has increased in every full season for which we have automated pitch-tracking data, with four-seamer speed rising from 91.8 mph in 2008 to 93.6 last season, teams have increasingly come to see the benefits of mixing in more slow stuff when a pitcher’s arsenal supports it. The Yankees, most famously, have taken fastball avoidance to the extreme, led by Masahiro Tanaka, whose “off-speed” stuff has become his standard speed. But the Yankees and Corbin are just the latest, greatest exemplars of a leaguewide trend away from certain types of fastballs (especially sinkers). The graph below lumps together four-seamers, sinkers, and cutters as “hard” pitches, and sliders, curves, changeups, and splitters as “off-speed” pitches. It reveals a subtle but steady decline in the former over the past decade.

The rate of “hard” pitches has fallen by about five percentage points since 2008, which equates to more than 35,000 pitches per season switching from fastball to off-speed. “Philosophies have changed over the years,” Haren says, adding, “Really, it’s about how many times can a pitcher throw his best pitch in the game” without endangering his health or impairing the pitch’s effectiveness because hitters are seeing it so often. More and more frequently, Haren explains, pitchers and teams are asking themselves the question, “Does a pitcher really have to establish his fastball?” And more and more often, they’re answering in the negative.

As Corbin’s slider rate has risen, Rockies reliever Adam Ottavino and Padres reliever Brad Hand have both pushed their slider rates above 50 percent, with Ottavino throwing his even when he isn’t ahead in the count, like Bizarro Nuke LaLoosh. Together, the two late-inning arms have combined for 20 2/3 innings and recorded 36 strikeouts while allowing nine hits, five walks, and three earned runs. Corbin, Ottavino, and Hand have all been effective before, but they’ve never sustained this level of dominance.

This embrace of breaking balls—which may be even harder for batters to hit when they’re geared up for faster and faster heaters—has contributed to another ongoing (and accelerating) trend that Corbin personifies: Pitchers are throwing fewer pitches inside the strike zone than ever previously recorded. The graph below shows the average zone rate by pitch type in 2018:

Across the board, “hard” pitches tend to be thrown in the zone more often than off-speed pitches. Throw fewer of the former and more of the latter, and the trajectory of the leaguewide zone rate starts to look like this:

A decade ago, more than half of all pitches ended up in the strike zone. Today, that rate has fallen below 47 percent. (Baseball Info Solutions data compiled by the company’s video scouts shows an even more massive decline, from 54.2 percent in 2002, the earliest available season, to 43.7 percent today.) Thus far this season, there have been about 307 combined pitches thrown on average per game. The difference between 2008’s zone rate and 2018’s means that about 11 more of those pitches are finishing outside of the strike zone. This GIF of leaguewide pitch locations in 2008 and 2018 shows greater concentrations of low pitches, particularly located away from a right-handed batter’s perspective—perhaps not coincidentally, prime slider territory with a righty on the mound.

From the pitchers’ perspective, all of this makes sense. When batters swing at pitches outside the strike zone, they’re more likely to miss, and whiffs don’t do any damage. They’re also more likely to make weak contact: Last year, batted balls on pitches outside the strike zone produced a .297 weighted on-base average, compared to .334 on pitches inside the zone. And as MLB’s home run rate has reached record highs over the past few seasons, pitchers have had even greater incentive to stay out of hitters’ hot zones. Maybe it’s working: The dingers and overall scoring have subsided so far this season amid pitchers’ continuing flight from the strike zone, although there are likely other forces at work. (Those factors include frigid temperatures—the average temperature is down 7 degrees compared to the same point last season—elevated pop-up rates, and possible changes to the ball.)

But a sensible strategy for pitchers comes with some side effects for spectators. The increase in pitches outside the strike zone has caused a corresponding increase in the length of the typical plate appearance, as pitchers—many of whom will be pulled before their third time through the order no matter how few pitches they’ve thrown—have grown fonder of nibbling or throwing “waste” pitches designed to get hitters to chase. Although the average number of pitches per plate appearance has been on the rise since 1988, the first year for which we have pitch-by-pitch data, the pace at which it’s climbing has picked up considerably since 2016. At this rate, the average plate appearance could pass four pitches as soon as next season.

Not only are plate appearances lasting longer, counteracting commissioner Rob Manfred’s attempts to limit the length of games (which have been one minute slower this season, albeit four minutes faster in nine-inning games only), but they’re also ending differently—and, depending on one’s taste, in less entertaining fashion. MLB’s strikeout rate, which has risen in each of the past 12 seasons, is up again, and by a lot, from 21.6 percent in 2017 to 23.0 percent so far this season. If that increase holds, it will be the second-largest year-to-year bump in strikeout rate ever, trailing only the increase from 1945 to 1946, when many major leaguers returned from military service. Because hitters don’t always give in to temptation, walks are also way up: The jump from last year’s 3.26 free passes per game to this year’s 3.59 would be the second-largest since 1910, and the largest since 1969, when the strike zone officially shrank. And as this year’s spring training stats presaged, the game’s rate of hit by pitches per game is also up to what would be its highest level ever in MLB’s modern era (1901-present), adding a possible safety risk to concerns about a stagnant playing style.

The net effect of all these extra pitches outside the strike zone, strikeouts, walks, and plunkings is a lower likelihood of the ball being put in play on the typical pitch. Even with balls flying over the fences less often so far in 2018, there have been 6.3 pitches per ball put in play this season, up from fewer than five pitches per ball put in play as recently as 1997, just before the previous intimidating rise in home run rate. As writer Joe Sheehan has noted, we may be in the midst of the first-ever calendar month in major league history with more strikeouts than hits.

Although it’s early enough in the season for some leaguewide stats to fluctuate, most of these developments aren’t surprising in light of what’s transpired in recent years. And while baseball is always evolving in one way or another, inevitably to someone’s overdone dismay, none of these changes seems likely to draw fans any closer to the edge of their seats.

What we seem to have here is a case of conflicting incentives. Pitchers have every reason to stay away from the strike zone. Lately, hitters have had every reason to swing for the fences. And teams have had every reason to seek out (or create) players who do both of those things. The only party that stands to suffer is the one watching from the stands and waiting longer for the next decisive pitch.

All stats through Wednesday, April 18. Thanks to Hans Van Slooten of Baseball-Reference and Rob Arthur for research assistance.