Sliders are tough. In 2010, the league threw just about 13 percent of its pitches as sliders. That year, the run value of a slider for a pitcher was 0.56 per 100 sliders thrown, the highest among all pitch types, and the only breaking pitch with a positive value. I don’t bring this up to mislead you: pitch-level values are a strange beast, because pitchers use their arsenals to set up and/or bamboozle hitters, and the slider may only have a positive value because it’s well set up by a fastball or similar. In any case, though, sliders were good, perhaps because they weren’t thrown very often, but they were good nonetheless. Fast forward to 2019. Slider usage has jumped substantially, and now sits above 18 percent (the gain has come mostly as the expense of sinkers; four-seam fastball usage has actually increased since 2010 as well). The usage increased year-to-year nearly every time, aside from a small drop in 2012 and a slightly bigger fall in 2014. Between 2018 and 2019, the slider rate increased by 1.5 percentage points, the bigger rise ever. Despite the increased usage, the value of a slider hasn’t really changed, from +0.56/100 in 2010 to +0.51/100 in 2019. The lowest value in this stretch was 0.46/100; the highest was 0.67/100. The slider’s value last season ranked it on par with the splitter, which tends to be thrown way less (only one to two percent of pitchers are splitters) and is more volatile year to year: 0.53/100 in 2010, 0.54/100 in 2019, minimum of 0.03/100, maximum of 0.54/100.
At this point, nearly everyone throws a slider: of the 158 starters with the most innings in 2019, two-thirds threw a slider over 10 percent of the time, and just 16 percent don’t have one in their arsenal. Of the 249 relievers with the most innings in 2019, over 70 percent threw a slider over 10 percent of the time, and just 14 percent don’t feature one. Analyses of “average performance of a pitcher that does/doesn’t throw a slider a lot” don’t tend to be conclusive, because at this point, pitchers without sliders mostly have something else going for them, or else they wouldn’t be surviving in the majors.
So, sliders are good, they’re tough, and they’re prevalent. Being able to handle sliders, whether that’s punishing them or just laying off of them and finding a better pitch to hit, seems like a big deal. That poses an interesting problem for Austin Riley, who was legitimately awful against sliders during his first season in the majors.
In 2019, 58 of Riley’s 297 PAs ended with a slider. His wOBA in those PAs was a puny .207, compared to his overall wOBA (still not great) of .307. This wasn’t a case of bad luck, either, as his xwOBA in those 58 PAs was just .184. In case it wasn’t clear from above, sliders are tough for everyone: PAs ending in sliders had an xwOBA of .269; PAs in general in 2019 had an xwOBA of .319. But, they were particularly brutal for Riley. Among players that had 50 or more PAs ending in sliders in 2019 (nearly 300 of ‘em), Riley had the seventh-lowest xwOBA and the 33rd-lowest wOBA. I want to be clear, so that what follows below is not misinterpreted: the slider was (and may continue to be?) a huge, huge problem for Austin Riley. Only Jorge Alfaro swung and missed at more sliders than Riley, in terms of percentage of total pitches seen. For sliders thrown low-and/or-away, here are Riley’s vitals: 106 pitches seen, 62 taken for a ball, two taken for a strike, five fouled away, and 37 whiffs. You read that right: no balls in play. Furthermore, no walks, as he whiffed on the only three-ball slider he got in that zone.
This isn’t a particularly hard issue to take note of, and Braves fans are probably particularly inured to the phenomenon, watching Dansby Swanson work through similar struggles for multiple seasons. Again, it’s also worth noting that Riley’s struggles might be more momentous in this regard, but they’re not weird: sure, Riley had a .000 wOBA/xwOBA on sliders low/away, but the league’s right-handed hitters only had a .175 xwOBA/.167 wOBA on them. The best Braves righty on those pitches was Josh Donaldson, with a .285 xwOBA, and he still struck out on them twice as often as he walked. Given this, it’s unsurprising that a very easy, convenient narrative sprung up: Riley couldn’t hit sliders, he terrorized the league, he got more sliders, he wilted. Bada-bing, bada-boom, we’ve explained his momentous rise and tragic fall in one easy story. That story gives rise a relatively comforting corrective action: teach Riley to lay off of (or punish, when he gets one) the slider, and enjoy delicious, cheap production at third base, with the sort of league-mauling upside he delivered in his first six weeks as a big-leaguer. Unfortunately, though, life is a little too complex for simple stories, and sliders are not the Austin Riley problem.
Demonstrating that Riley has more things to work on than just sliders is not too hard, but before I do so, I want to throw up some background information on Riley that makes the explanation clearer. For me, Riley’s debut season can really be broken down into two parts: the awesome first part, and the really-not-awesome second part. As far as a breakpoint, my preferred target is June 29:
Riley started out raking. It was never going to keep up (he wasn’t Mike Trout), and even some of those early homer-driven successes had ameliorated down to a wRC+ in the 140s in mid-June. Riley was able to maintain that level of production for in mid-June thanks to a nine-game stretch in which he had a wRC+ near 200, and then rebounded after a brief six-game skid to hit homers in back-to-back games against the Mets. And then, pretty much the inexorable decay in his batting line took hold. June 29 was the last time his season-long wRC+ was above 130; after July 24, it never exceeded 103. (It ended at 84. Oof.)
If you wanted to make the case that the league realized that Riley was abusing fastballs and needed to see a steady diet of sliders, you’d probably figure that overlaying the rate of sliders he saw would tell the tale. And, well, it doesn’t.
For the season as a whole, Riley saw 25 percent sliders. The cumulative rate of his sliders was inconsistent, but it doesn’t track to his overall hitting slide. He saw mostly fastballs early on and punished them, but the big slider spike came a bit after his first decline, and his small skid in June came as his slider rate decreased. Starting in July, he saw a fairly similar rate of sliders (bouncing around between 24 and 27 percent), but his hitting line just got worse and worse. Weirdly enough, the cumulative four-seam fastball rate almost seems to tell a better-aligned story in this regard.
For those of you that like looking in tables instead of charts, the below should be instructive, using June 29 as a cutoff point.
Riley was bad against sliders. He got worse against sliders, but he actually whiffed a bit less on them and also saw fewer of them in his brutal second act. The real difference, of course, is that he went from destroying four-seamers to being destroyed by them. His whiff rate went up, and he had to contend with a greater proportion of them as well.
There are a lot of avenues to go from here, but they mostly just reiterate the above. Plotting a more granular against-sliders wOBA/xwOBA/whiff rate shows that Riley’s struggles with sliders were fairly common and not localized to the latter half of his season. Examination of fastball velocity and location doesn’t have any smoking guns, only that Riley just started being eaten up by fastballs where he previously crushed them. In what I call the “power cross,” (all portions of the strike zone except the ones nearest the four corners) Riley had a .467 xwOBA and a .601 xwOBACON (xwOBA on contact) versus fastballs through June 29. For the remainder of the season, those numbers were .174 and .261, respectively. The whiff rate on what should be relatively easy-to-hit pitches went from 22 percent (already high, but that comes with the power tradeoff) to 30 percent, and the quality of contact when whiffs weren’t happening plunged severely. Pitchers weren’t really throwing Riley harder fastballs in the second half, nor differently-placed fastballs... he just wasn’t mashing them. Probably the most telling tiny-sample stat: on down-the-middle four-seamers, Riley had two whiffs and three hits (including a homer and a double) through June 29 out of 13 pitches; after that date, across 12 pitches, he had five whiffs, and one of his two balls in play (neither went for hits) was a grounder. It’s only a few pitches, but when you’re not killing the gimmes, it’s that much harder to prop your batting line up using only pitcher’s pitches.
Hitting isn’t easy. Even improving against one devastating pitch type seems like a monumental task. But, the challenge for Riley goes beyond just fixing his season-long struggles with sliders. Riley’s ability to hit the fastball fell apart as his season trended downward. Maybe it fell apart because he was so focused on the slider, he couldn’t gear up to mashing the four-seamer. But, he saw fewer sliders and more four-seamers, and never seemed to revert to his original, fastball-killing protocol.
Even if there is something to the idea that wariness of the slider lowered his ability to hit fastballs, it seemed to play out in interesting ways. Consider the pitch mix Riley saw by count, again separated by the June 29 breakpoint.
These two graphics look similar, with the most notable difference being a switch to fastballs in 1-0, 2-0, and 2-1 counts. Even when Riley was getting ahead, pitchers were throwing him fastballs, and getting away with it. Through June 29, about 18 percent of pitches Riley saw were in those three counts, and he had a .396 xwOBA when ending the PA in that count, along with an xwOBA above .500 on four-seamers. Afterwards, the frequency of those counts didn’t change (still about 18 percent), but the effectiveness did. The xwOBA plunged to .219, with an egregiously bad .069 against four-seamers.
Even in counts where Riley, by basic baseball processes, should have been looking for the fastball, he failed to do anything against the fastball. Pitchers responded by throwing him more fastballs, which he couldn’t do anything with.
Austin Riley can probably live with a slider issue. Rhys Hoskins is an example of a player that has struggled against sliders, and sees a fair bit of them, and still hits at a clip well above league average. In recent history, Matt Carpenter, Eddie Rosario, and Miguel Sano are other slider-strugglers with strong degrees of offensive success. What Austin Riley probably can’t live with is a pervasive fastball issue. Over the last three seasons, only six (out of 1,202!) player-seasons have had a lower xwOBA against four-seam fastballs than Riley’s .212 mark between June 30 and the end of 2019. The highest wRC+ for any of these six players in any of the last three years? 105. The average? 56. If fixing whatever slider ailment helps Riley go back to killing fastballs, great. Otherwise, it may be worth suggesting that attention should be paid elsewhere.
(Luckily, I haven’t seen any reporting that Riley is specifically working on slider issues. The limited information that has come out has suggested that Riley’s offseason work is more holistic in nature with respect to his swing. I don’t mean to imply that Riley and the Braves are doing anything wrong, only that while sliders may be a problem, they are not the problem as far as Riley’s viability for 2020 and beyond.)