To take a step forward in 2022, Aaron Ashby must trust his sinker

Aaron Ashby’s 4.55 ERA (107 ERA-) may not look impressive, but his debut season should be considered a success.

First of all, he performed far better than that ERA suggests. The top prospect posted a 3.03 xERA, 3.58 FIP, 3.18 SIERA, and 84 DRA-. His 29.3% strikeout rate and 61.3% ground ball rate were excellent. Secondly, Ashby allowed 13 of his 20 runs in two of his 13 outings. He coughed up seven runs in his MLB debut and another six in his final regular-season appearance, both of which lasted under an inning. In between was a 30-inning stretch with a 1.78 ERA and 2.64 FIP.

The bottom line is that Ashby’s stuff plays at the game’s highest level.

In particular, his slider looks like a top-tier pitch. Opponents batted just .077 with a .148 wOBA while whiffing on 42% of their swings against it. Ashby allowed just three hits against it, the only extra-base hit being a home run by Trea Turner in his final regular-season appearance.

Ashby’s slider averaged an elite 42.5 inches of drop, which means it has more of a slurve-like shape than a traditional slider.

Ashby also demonstrated a promising changeup, which bodes well for his ability to retire right-handed hitters. In fact, he threw each of his 114 changeups to righties. Clocking in the high-80s, the sudden drop and slight fade on the pitch make it tough to handle for hitters, especially if they are anticipating a slider or a fastball.

The changeup dismantled hitters to the tune of a .167 average, .216 wOBA, and 35% whiff rate.

As excellent as those two pitches are, Ashby’s sinker looks just as nasty by the eye test. The southpaw can generate so much movement that the pitch can sometimes look like a screwball.

That movement pairs exceptionally well with Ashby’s slider.

A pitcher with Ashby’s arsenal would typically use the sinker as his main offering. It would be his go-to pitch for establishing himself in the strike zone, getting ahead in the count, and getting back in the zone when he falls behind. The slider would be his wipe-out pitch with two strikes, and the changeup might be sprinkled in once or twice during an at-bat to keep the hitter off-balance.

That’s not how Ashby operated. He utilized his slider as his leading pitch. 39% of his pitches were sliders, 34% were sinkers, and 21% were changeups. He occasionally showed his curveball and four-seam fastball but mostly tucked them away as he worked primarily out of the bullpen.

The reliance on the slider increased dramatically after Ashby’s debut. In that outing, he threw almost exclusively sinkers (82%) as he battled his control and tried unsuccessfully to settle in. In subsequent appearances, the 23-year-old leaned on his slider at a 42% rate compared to just 30% sinkers.

Not only was his overall slider usage much higher than that of his sinker, but after his debut, Ashby preferred his slider in just about every count situation.

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Perhaps most odd is that Ashby shied away from his sinker the most when he was behind in the count. Whereas most pitchers turn to their fastball when they need to find the strike zone and get back into the count, Ashby distanced himself from it. Instead, he leaned harder into his slider.

That unorthodox approach starts to make more sense when you look at how Ashby’s sinker fared in his first season in the big leagues. It yielded a .333 batting average, .375 wOBA, and an underwhelming +5 run value, according to Statcast.

Due to their movement profile, sinkers rarely induce many swings and misses. Instead, their calling card is coaxing weak contact. However, Ashby’s sinker was even less prone to whiffs than usual. Just 12% of swings against it came up empty. The league average is about 16%. Ashby also generated called strikes with his sinker at a lower rate than his contemporaries (15% versus 20%).

The underwhelming 22% called strike plus whiff rate of Ashby’s sinker stemmed from poor control. This is not a new issue for the left-hander, who posted walk rates of 12% and 9% in Triple-A and the big leagues, respectively. He often chucked his sinker right over the plate instead of burying it low in the zone.

It makes sense that Ashby threw fewer sinkers when behind in the count. It simply was not a good pitch to throw in such situations. His control was inconsistent, and he often left it over the plate. Hitters rarely took it for a called strike. When it was in the zone, they swung and typically put it in play. You should not expect great results throwing a pitch with those qualities in a hitter-friendly count.

In 2022, Ashby will need to start trusting his sinker more. Developing better control will go a long way in that regard, but he doesn’t have to become Greg Maddux. Even without always having pinpoint location, Ashby’s sinker has the makings of a highly effective pitch.

Even though Ashby often put it in an unfavorable spot where many sinkers flatten out, opponents still struggled to square it up. It induced ground balls at a whopping 70% rate. Hitters averaged a -7-degree launch angle, 5% barrel rate, and 87 mph exit velocity when they put it in play. A .252 expected batting average and .329 xwOBA indicate that given their poor quality of contact, they should not have collected as many hits as they did.

Hitters expanded the zone a bit more against Ashby’s sinker (28.4% chase rate) than usual, which points toward its movement and life. It also suggests that better location could lead to more off-balance swings, broken bats, and possibly more swings and misses. Slightly improved control could go a long way.

Against lefties, Ashby can use his sinker in a traditional fashion by getting in on the hitter’s hands to induce grounders. He can get more creative against righties. In the GIF above, he starts the pitch at the bottom of the zone on the outer third of the plate so that it moves down and out, working similarly to a screwball.

The movement and velocity of Ashby’s sinker make it difficult to square up. Improving his control and comfort with it will only make it more effective and make him less reliant on his slider.

Ashby will get important outs for the Brewers in 2022, but what capacity those outs come in remains to be seen. He could resume middle relief duties while being on hand for the occasional spot start, but there is a path for him to become a regular rotation member. The club may want to continue using a six-man rotation as they did last year. If they fail to re-sign Brett Anderson or add another veteran starter, Ashby is an obvious candidate to round out the group.

Whatever role he is in, Ashby’s sinker will play a significant role in his level of success in 2022 and beyond. The top prospect’s stuff plays at this level. His slider and changeup are fantastic pitches. Having a highly-effective sinker that he trusts will allow him to take the next step.

Statistics courtesy of FanGraphs, Baseball Savant, Baseball Prospectus, and Pitcher List.