Major League Baseball is changing. The ground is moving beneath the feet of owners, players, writers and fans. In some ways, these changes are obvious. They’ve defined the last few seasons and postseasons, and some changes that could be coming over the next year could do so even more plainly. There was the arrival of Statcast in late 2014, the juiced baseball of late 2015, ’16 and ’17, the tension-filled winter of 2017-18 and the rapid marginalization of the starting pitcher. There was the slow, then fast, then utterly ubiquitous spread of defensive shifts, and there were revolutions in both pitching (toward more high, four-seam fastballs) and batting (toward more efficient ways to lift the ball and hit homers). There remains the specter of various pace-of-play measures, including pitch clocks and starting half-innings with runners on base once games reach extra innings.
While many of these changes are easy for even casual fans and commentators to observe and understand, others can be difficult to notice, let alone to fully appreciate. For instance, consider the relationship between the sinker and the slider. In the decade-plus during which we’ve had detailed pitch classifications for virtually every pitch thrown in the majors, the four-seam fastball has been the most common offering every year. For many of those years, it’s also been the case that the sinker (what some call a two-seam fastball) has been the second-most common. Sinkers, well, sink more than four-seamers do, and in virtually all cases, they also move more laterally, in the direction of the pitcher’s throwing arm (so, for a righthander, further in on a right-handed batter), than do four-seamers. Both of those properties make them pretty good at inducing ground balls, at least against the right batters, when located well.
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Technically, the sinker’s natural counterpart is the cutter, a near-fastball that swerves the opposite direction laterally. In practice, however, cutters have always been relatively rare, because most hurlers find that the pitch exerts some measure of extra stress on their elbow, and because it can be tough to execute consistently as a distinct offering from a four-seamer. That’s why the slider, which — in terms of grip, arm action and mentality — is practically just a cutter thrown at something less than absolutely maximum effort, has long been the primary complementary pitch to the sinker.
As batters have adapted their approaches to the reality of the modern game, however, they’ve forced pitchers to change, too. As recently as 2014, scoring was at a near-historic nadir, and the global ground-ball rate was as high as it had been in decades. Pitchers were pounding opponents with sinkers and consistently inducing weak contact with them. Thus, many hitters began a systematic counter-adjustment: They traded contact for steeper swing paths, laid off pitches they couldn’t handle and focused on being able to lift and drive sinkers at the bottom of the zone. In essence, many MLB hitters’ swings and approaches are now engineered specifically to make sinkers ineffective — to punish that pitch, and take it away from opposing hurlers.
That’s one impetus for what has been a jarring change in the league’s collective pitching approach, one that has seen the league go from throwing about 55,000 more sinkers than sliders every season to throwing more sliders than sinkers — in just four years. Another is the implementation (and the enormous analytical potential) of Statcast. The timing of the shift helps illustrate that. Since 2015, every team has had the ability to gather and deconstruct unprecedentedly detailed information about pitchers’ release points, and about the physical characteristics of each pitch.
“Spin rate” has gone from an obscure concept mentioned occasionally by pitching-focused scouts to a catchphrase that pervades the discussion and analysis of pitching by outsiders and insiders alike. It’s most often associated with the fastballs of certain pitchers whose otherwise unexceptional heaters inexplicably defy gravity and seem to “hop” over hitters’ bats, and with the league’s most mesmerizing power curveballs. But the spin rate on a slider matters a lot, too, and teams have found that the data they can glean on pitchers’ sliders using Statcast provides an opportunity to redesign the pitch altogether, or to optimize its use.
Teams use spin rate, arm slot and other data on the flight of the ball to identify hurlers with those great fastballs and curves, and it’s still perfectly possible to peg a hurler as a good candidate to bring along a changeup just by watching him. Data informs which pitchers teams attempt to acquire, and how they advise those pitchers to use certain pitches. They might encourage some guys to attack the top of the zone more often with one of those rising fastballs or invite them to throw their curveball more often because of its half-hidden brilliance.
Sliders, however, offer an even more intriguing opportunity. With the data teams now have, they can work with pitchers to reshape sliders, to transform them from loopy to sharp, to change the plane of their break. It’s even possible, it would seem, to create a slider from thin air. The Twins’ Taylor Rogers is an illustrative example. Typically reliant on a combination of sinker and curveball that made him very susceptible to right-handed batters, the southpaw added a slider to his repertoire at the end of May. From that point on, the only pitcher who allowed an on-base percentage lower than the .206 opponents had against Rogers was A’s closer Blake Treinen. Of the 170 batters Rogers faced from June 1 through the end of the season, 57 struck out.
The secret wasn’t necessarily throwing the slider all the time. It was about using that pitch to make batters uncomfortable, allowing them fewer chances to attack the ball. One problem with the sinker, especially when a pitcher uses it as a primary fastball, is that it doesn’t work well with other pitches. Almost without exception, a sinker and a curveball will look different right out of the pitcher’s hand, giving opponents an earlier chance to decide whether or not to swing (and whether to wait back on it or go get it as quickly as possible). Sinkers and changeups look much more similar out of the hand (they spin on the same axis), but often, they move about the same amount, in about the same direction. So unless there’s a tremendous differential in velocity, the batter can still make good contact, despite technically being fooled.
Rogers embodies this. His curveball and sinker didn’t play off one another in a way that kept hitters on the defensive. Adding the slider left hitters guessing much more often, and they were wrong much more often. No pitcher who threw 100 or more sliders induced swings on a higher percentage of those pitches than did Rogers. That pitch, after all, breaks in the same general direction as the curve and is thrown with an arm speed much more akin to the sinker. Having the slider made Rogers more deceptive, leading not only to more strikeouts but to more ground balls, too.
Being able to build a slider from scratch remains, of course, the exception, rather than the rule. Rogers’ teammate Kyle Gibson is a more typical case study in the power of modern pitch design to change the way a slider works. From 2015 through 2017, Gibson’s slider had a fairly constant movement differential of just over six inches (horizontally) and about 7.5 inches (vertically) from his fastball. In 2018, however, he increased that vertical movement differential to almost 9.5 inches. A subtle change in the way he threw both pitches let him tilt the slider down more, and that increased two-plane action turned his slider into a bat misser (over 27 percent of all his sliders resulted in an empty swing). Gibson’s 3.62 ERA was over a run below his career mark, and his 21.7-percent strikeout rate blew away his 16.0 career mark.
Famous tinkerer Trevor Bauer, who junked a true slider in 2015 in favor of a cutter that he could throw harder but less frequently, brought back a slower version in 2018, with dramatic sweeping action (over a foot of lateral break, on average, relative to his fastball) and dramatic results: The pitch induced whiffs at a career-best rate. On the brink of free agency, Patrick Corbin had the true breakthrough season for which he’d hoped for years, using a slider more often and leading MLB in whiffs per swing on the slider by generating more downward movement even as he threw it harder than ever. Eight different pitchers threw at least 200 sliders and averaged 90 miles per hour or harder on the pitch, up from three such hurlers in each of the two previous seasons.
There must, surely, be some point at which the returns of throwing more sliders begin to diminish. So far, though, the league has not reached that point, or even approached it. The slider induces more whiffs per pitch and more whiffs per swing than any pitch other than the splitter, a much rarer specialty. The distance between the mound and the plate just doesn’t provide batters the margin for error necessary to adjust to two-plane movement generated by a high spin rate and a slightly altered spin axis, out of a release otherwise virtually identical to that of a fastball. Batters made contact on 68.3 percent of swings against sliders in 2008. In 2018, despite seeing the pitch about 45 percent more often, the league made contact on 64.5 percent of swings.
Batters are getting bigger, stronger, smarter and faster, all the time. The fences aren’t getting farther away, and the foul lines aren’t pinching slowly in from their perpendicular positions. Despite the global increase in velocity and the increased focus on intensity instead of workload, pitchers are under siege — indeed, under mortal threat, since a line drive hit 115 miles per hour back through the box has a real chance of killing a hurler who can’t get his glove up or his head down in time. Strikeout rates continue to rise league-wide because pitchers can’t reliably get these phenomenal athletes out in any other way, and if the strikeout is the only really desirable outcome, the slider is the natural weapon of choice. Throughout MLB, pitchers are discovering dozens of different ways to deploy that weapon, and it’s working for almost all of them.