The Rise of the All-Slider Outing

Amir Garrett emerged from the bullpen into quite a jam. With the Reds up 5-1 heading into the eighth, all had seemed fine, but Michael Lorenzen allowed the first three batters he faced to reach base. As Garrett prepared to face Anthony Rizzo, one swing of the bat could tie the game. Knowing that, Garrett didn’t mess around — he went to his best pitch right away.

The first slider he threw might have clipped the inside edge of the zone, but it was called a ball. Still, down 1-0, he didn’t give in. He went back inside with a slider — and hit Rizzo. That free base drove in a run, and now Garrett was right back where he started with one less run to work with.

With free-swinging Javier Báez up next, it was time for another slider. Garrett again clipped the corner, and this time was rewarded with a grounder that Joey Votto threw home for a force out. Garrett breathed a sigh of relief. There was no time to relax, though — with only one out, the situation was still precarious.

Ian Happ, coming off of a scorching-hot six game stretch where he had compiled a 343 wRC+, stepped in next. Fortunately, though, Happ has one major weakness: sliders. Garrett took no prisoners:

Home stretch now — only Kyle Schwarber left to retire to escape the jam. Schwarber is a tremendous fastball hitter, so Garrett had no choice: one last slider induced a groundout, and Garrett celebrated with a light backwards jog as he wriggled free of a tough inning:

That inning might not have seemed like much, but it’s emblematic of a trend that’s been slowly creeping into baseball — the all-slider outing. As pitchers use off-speed pitches more and more, the name “secondary” makes less sense than ever. Garrett’s four batters and seven pitches of slider-only baseball are a bit much, even in today’s game, but he’s not alone.

While no one has faced or retired more batters in a single outing than Garrett has using only sliders, teammate Robert Stephenson and the Mariners’ Matt Wisler each have nine-pitch outings that only featured sliders, facing three batters each. Wisler has two other games where he threw four pitches that were all sliders.

There have, as of yesterday, been 18 outings where a pitcher threw at least four pitches and nothing but sliders. Half of them are one-batter outings, and that’s easier to wrap my head around — when a lefty specialist comes in to face a dangerous slugger, the slider treatment makes sense. If ever there was a time to throw only sliders, it’s for one batter from a same-handed pitcher.

If that seems standard to you, though, it isn’t. In 2014, there was exactly one appearance of four or more pitches where the pitcher threw only sliders — Dana Eveland striking out Shin-Soo Choo, if you’re curious. There were only 16 all-slider outings total, and six were single-pitch outings, which hardly fits the spirit of the all-slider appearance. There have been 73 so far this year, 29 of the one-pitch variety. It’s the year of all slider everything.

These all-secondary outings are interesting, but they’re small potatoes. Who really cares if Amir Garrett threw seven sliders or seven sliders and one fastball? The trend is the same on the starter side, though. Using 2014 as a baseline again, there were 109 games where a starter threw 40 or more sliders. There have been 133 of those games already this year, with more than a month left to play in the season.

That increase sells modern baseball’s slider reliance short. Pitch limits weren’t nearly as prevalent then as they are now. Those 109 starts average 126.7 pitches — these slider-reliant pitchers threw 34.8% sliders. They only got to 40 sliders by sheer volume. There was exactly one game where a pitcher threw 50% or more sliders — Erik Johnson tried it in Coors Field to predictably poor effect. The only other pitchers to throw 50 pitches in a game with at least 50% sliders were George Kontos and the immaculately named Stolmy Pimentel.

In comparison, 2019 is beset with 50% slider-using starters. There have been 25 half-slider starts this year, and another 14 50-pitch relief outings that fit the bill. This doesn’t count openers, either — I used a 50-pitch minimum for starts to exclude that particular gimmick. Recently released Jhoulys Chacín alone has 12 such starts, and some of the other pitchers to do it are big names. Clayton Kershaw has one this year. So do Jacob deGrom and Patrick Corbin. Chris Sale has one, and just missed another with a 49.4% slider start.

If it feels like the pitch is taking over baseball recently, you’re not wrong. From 2002 to 2016, the league-wide slider percentage was between 11.8% and 15.3% every year. In 2017, the dam broke; 16.3% sliders, then 16.9% in 2018, and finally 18.2% so far this year. Throw in cutters, which are basically harder sliders, and that percentage rises to 24.3%, up from a previous-era high of 20.3% in 2011.

The reason there are so many sliders is pretty straightforward. Teams are increasingly doing the math and realizing that pitchers throw too many fastballs. Sliders have been the most effective pitch on a per-pitch basis nearly every year since we’ve calculated pitch values. The implication is clear — cut fastballs, add sliders, profit.

What’s striking to me, though, is that there doesn’t seem to be any efficiency loss that comes with throwing all sliders. Nearly every pitch displays diminishing returns to some degree. Four-seam fastballs have never been worse, on a per-pitch basis, than they are this year. The reason for that is partially home runs, but it’s also partially that every team is rushing out to have their starters throw four-seamers.

The more marginal hurlers pick up four-seamers, the more bad four-seamers there are, and the worse the pitch looks on a league level. The same has been true to a lesser extent for the recent spike in curveball usage. When pitchers abandoned sinkers by the boatload, the per-pitch value of sinkers went up — only the best sinker-ballers remained.

Sliders have, so far, been mostly immune to this effect. While they’ve lost a bit of value, they’re still the best pitch in baseball this year by linear pitch weights. There’s surely a theoretical tipping point, where enough maladroit pitchers add below-average sliders to their arsenals that league-wide slider outcomes deteriorate, but we haven’t reached it yet.

One of the reasons for this is that instead of bad pitchers switching to a slider, we’re increasingly seeing pitchers with already-effective sliders throw them more often. Take a look at the ten starters who lean on the pitch the most:

There are some bad pitchers on the list, but no one with a bad slider, as you can see from the ambitiously-acronymed wSL/C (pi) column. As long as the added sliders are coming from pitchers like Kershaw and Sale, both of whom are at the forefront of the slider movement, there’s probably room for the league to add more sliders.

The real innovation in all of this is the blurring of what is and isn’t a secondary pitch. Growing up, I always intuitively understood that breaking pitches were harder to hit than fastballs. I also knew intuitively that pitchers weren’t supposed to throw them too much, and I never bothered to reconcile those two in my mind. It was known, and no one thought to question it.

That era of baseball looks to be over. Amir Garrett can come in and throw sliders until he’s done. Lance McCullers Jr. can throw 24 straight curveballs in a postseason game. Jacob deGrom can throw 55 sliders in a 105-pitch start. Why shouldn’t they throw their hardest-to-hit pitch as often as they can?

There’s still some upper limit. No one’s going to throw a 100-pitch game with only sliders any time soon. They probably won’t throw a 20-pitch game with only sliders sometime soon. But that upper limit is far higher than we thought for almost all of baseball history, and pitchers are increasingly pushing that limit higher.