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No-Fly Zone, with Aaron Bummer

Getting the southpaw setup expert back to 2019 results, with a simple tweak.

Division Series - Astros v White Sox - Game Three Ron Vesely/Getty Images

One hot topic among White Sox fans to start the season has been the rollercoaster Aaron Bummer has taken us on in his first three appearances of 2022.

Bummer’s results in the past year or so, while solid, have been underwhelming to many. In this piece, I’m hoping to outline what makes Bummer so special and where his issues (although minor) may be coming from. I also have a plan for how to get him back to the elite lockdown level he is capable of.

What Makes Bummer Special

In 2019, Bummer put together a breakout season. He finished 10th in ERA among all relievers, with the second-highest ground ball rate behind Zack Britton. The White Sox rewarded this performance with a five-year, $16 million extension.

After dealing with injury in 2020, Bummer upped that GB% to 76.9% in 2021 — tops in the majors.

One of the things I like best about Bummer is when he isn’t beating himself with free passes, it takes three good swings to beat him. Home runs, or even extra base hits, aren’t something you have to worry about.

Bummer ranked 15th among relievers in lowest HR/9 at 0.48. Of those above him, the highest HR/FB rate was 6.8%. This means that of the fly balls that pitcher gave up, 6.8% of them left the yard. League average is around 10%, and this stat can vary heavily year to year for an individual. A pitcher can control limiting fly balls, but of the fly balls that are hit, pitchers have less control over whether they are hit well enough to leave the yard. Bummer’s HR/FB% was 17.6%, and despite this abnormally-high rate, he finished among the Top 15 in baseball when it came to limiting HRs.

By contrast Liam Hendriks, while absolutely dominant in his own right, has been a bit more prone to the long ball, which can tie a game in a hurry. He was almost three times as likely to give up a home run last year than Bummer.

Bummer’s bread and butter has always been his 95-97 mph sinker. It generates ground balls at an exceptional rate, and per Driveline Baseball’s stuff+ metric, ranked tops in baseball among sinkers at 91% better than league average. Movement-wise, Bummer’s sinker generated 37% more drop than league average. Not only is this sink due to a low arm angle and low spin rate, but a big portion of it is due to seam-shifted wake, a topic that is still being explored by the analytics community.

I’m not going to pretend to be an expert on it, but basically, seam-shifted wake is the difference between how the ball SHOULD move solely based on its spin characteristics, and how it ACTUALLY moves. The difference is due to the fact that the baseball isn’t just a sphere, but it has raised seams, leading to air acting on it slightly differently than if it were smooth. This is an added facet of deception, as hitters have been reading spin and trajectory their whole lives — so with seam-shifted wake, the ball is ending up in a slightly different place than the hitter’s brain is telling him it should.

For further explanation, refer to this video to get a glimpse at how hitters must feel stepping into the batter’s box against Aaron Bummer:

As a hitter, the more thoughts going through your mind in the box, the harder it becomes to hit. I guarantee many hitters enter the box against Bummer focusing on trying to hit the bottom of the ball, knowing they are likely to swing over it or ground out if they don’t compensate for the movement of Bummer’s sinker.

But wait, there’s more! Starting last year, hitters aren’t able to just sit on Bummer’s sinker and dedicate their entire focus to somehow getting this pitch in the air. Now, Bummer’s slider is now something hitters have to dedicate mental space to as well.

In 2019, Bummer’s strikeout rate was around league average. In 2021, he introduced an absolutely devastating slider, a pitch that metrics back as one of the most unhittable pitches in baseball. The pitch ranked ninth in Whiff% of any slider in the game, starter or reliever.

So, Bummer has a sinker that hitters pound straight into the ground, and a wipeout slider that generates swings and misses at an elite rate. What did this boil down to in 2021? An astounding 85% of at-bats vs Bummer ended in a strikeout or ground ball — tops in the bigs, by 7%.

Bummer’s 2021 Percentile Rankings
Baseball Savant

Bummer’s BB Bugaboo

However, even with this pitch combination, Bummer’s results were surprisingly not as elite as the metrics would suggest. He still had a solid season, but despite the addition of a slider that should have pushed him into elite territory, 2021 was a slight step down from 2019. Two main reasons for this that can’t be ignored were horrible batted-ball luck, and suboptimal infield positioning, which Patrick Nolan over at Sox Machine explored at the end of last year.

However, as Steve Stone loves to remind us, with Bummer, it always comes down to throwing strikes. In 2021 and to start 2022, Bummer has walked more than his fair share of hitters, leading to dangerous situations and “nickel-and-dime” runs crossing the plate. Bummer’s walk rate in 2019 was 9.2%, and since then, it has been 12.6%. To break it down in a BB/inning format, in 2019, he was allowing a free pass around once every three innings, and since, he has averaged over a walk every two innings.

Bummer is a super interesting case to me, so I wanted to do some digging to find an explanation for these frustrating walk issues. From the eye test, it looks like Bummer has struggled to get ahead in counts to start 2022 due to a lack of sinker command. Bummer has an unorthodox motion, and he has talked in the past about working to get everything in sync and drive towards the plate rather than getting too side-to-side with his momentum.

Knowing this, I first checked out his release point to see if that would uncover any clues, as a varying release point can lead to control issues.

Sure enough, per Baseball Savant, the vertical release point of Bummer’s sinker has steadily dropped over the past three years. My thought was that the implementation of the slider may have led to bad habits, affecting his sinker command. However, after doing more digging, Bummer’s zone percentage with his sinker actually stayed basically the same between 2019 and 2021, around 55% per Alex Chamberlain’s Pitch Leaderboard.

So, Bummer still throws strikes with the sinker at the same rate, disproving my theory about release point issues. The only difference between his repertoire in 2019 and now is the slider going from 3% usage to 30%.

Baseball Savant

This is where it clicked for me. Bummer only throws the slider for a strike 35% of the time, pulling his percentage of pitches thrown in the zone down from 46% to 42% and the batter’s swing percentage down from 47% to 42%. Even more importantly, the slider leads to way more swings-and-misses than the sinker, which typically generates contact early in counts. Swings-and-misses lead to deeper counts. Deeper counts lead to more walks. Basically, the fact that the slider is so tough to hit can, at times, hurt Bummer when it comes to issuing free passes.

An Altered Plan of Attack

Keep in mind, the walks, in the scheme of things, don’t take away from the fact that Bummer is one of the top relievers in the game. As mentioned, quite a bit of 2021’s issues can be explained by poor luck and positioning. However, I would recommend Bummer changes his arsenal a bit depending on situation. With the bases empty or a man on first, a walk ends up in the same result as a ground ball single through the infield. In these situations, I would recommend a pitch selection a bit closer to the 2019 approach, relying more on the sinker and less on the slider, and focusing on generating contact on the ground. This will not only lead to fewer deep counts, but also increase the possibility for double plays — a staple of Bummer’s 2019 season.

When runners do get into scoring position, that is the opportunity to go to the slider more to generate the swings-and-misses that will keep those runs off the board. His slider is an absolutely awesome pitch, especially when used in the correct situation. Bummer has already used the pitch to work himself out of a few jams in 2022.

Chime in with your thoughts, as I know Bummer has been a bit of a lightning rod for commentary this year. The tools are all there for him to be one of the most dominant relievers in the entire sport.