An Analysis of Jakob Junis, Arsenal Distribution, and Pitcher Individuality

The outlook for Jakob Junis was bleak, to say the least. After opening his 2021 campaign with four solid starts, Kansas City Royals Manager Mike Matheny sat the right-handed pitcher down in his office and informed him of the team’s plan to move him to the bullpen. Jakob Junis, who sported a 3.47 ERA through 23.1 innings at the time, was rightfully surprised, as a demotion from the starting rotation to the pen often comes after a string of poor outings. Nonetheless, this managerial decision would foreshadow the rocky road ahead in the relationship between Junis and the Royals. 

Matters took a turn for the worst after Junis allowed 9 earned runs in his first 6 innings out of the pen. On June 6^th, the Royals optioned Junis to their Triple-A affiliate. He proceeded to throw 4.2 more innings for the big-league club before happily electing to proceed as a free agent. The decision was a rather easy one for the 29-year-old pitcher, as he publicly stated, “To say things ended well over there would be a lie.” 

Junis’ tenure with the Royals organization had spanned over decade, having signed out of high school in 2011. Despite a remarkable high school career, Junis’ fastball was never his strong suit. According to scouting reports, Junis’ fastball sat in the high 80s, low 90s range—enough to dominate the high school baseball circuit, but a few ticks below the Major League standard.  

What was his strong suit? His slider. Junis’ slider is and has always been his most productive pitch, and it wasn’t remotely close. To put it into perspective, in his time with Kansas City, Junis’ slider recorded a run value of –25. That was his only pitch with a cumulative negative run value across his five seasons with the Royals. Even in Jakob Junis’ turbulent 2021 season, his slider generated a remarkable 40.2% whiff rate. It wasn’t only his best pitch; it was one of the better pitches in the league.  

Characteristically speaking, the pitch falls into the “sweeper” category of sliders, generating approximately 12 inches of sweep. As is the case with most sweepers, Junis’ slider approached the plate at a rather steep horizontal angle that often approached 4.00° (nearly one degree steeper than the league average slider). A general principle for breaking balls is that velocity and spin-induced movement come at a trade-off. The hardest-thrown breaking balls possess a ton of gyro spin and induce little spin-based movement. The slower breaking balls are often the loopy curveballs with south of –10 inches of induced drop. Junis’ slider drastically evolved over time. From 2020 to 2021, Junis sacrificed 4 inches of sweep for nearly 3 MPH. As a result, his whiff rate and chase rate both rose dramatically. 

If Jakob Junis possessed such a dominant pitch, why couldn’t he sustain success at the MLB level? Well, the Royals development system evidently fell victim to old school baseball philosophies that preach the importance of establishing one’s fastball. For the flame-throwers who pump triple digits with above-average lift, this motto may hold true. However, Junis did not fit that mold. Not only was his velocity comfortably below average, but his fastball shape was ineffective as well. To put it bluntly, his fastball was a bad pitch. And that bad pitch consumed over a third of his pitch distribution.  

MLB hitters destroy fastballs. In 2022, the league average wOBA against fastballs is .340, compared to .276 against offspeed and .270 against breaking balls. MLB hitters are like sharks. The same way sharks can smell blood from a distance, MLB hitters can smell a bad fastball from a mile away. They took this to the extreme against Junis. Earlier, I stated that Junis’ slider recorded a run value of –25 in his five seasons with the Royals. Across that same time span, his fastball posted a run value of 23, and a .407 wOBA against. Not only was it a bad pitch; it was a bad pitch that hitters hammered.  

In Junis’ defense, I wholeheartedly believe that this was not his fault. He is not cut out to throw a four-seam fastball. A strong indication that a pitcher is not cut out for a traditional four-seamer is if their four-seam spin efficiency falls in the 70%-90% range. Some of the sport’s most dominant pitchers fall into this mold, such as Max Fried, Noah Syndergaard, and Tanner Houck. From a mechanical standpoint, this usually means that the pitcher struggles to stay behind the ball. We often refer to these pitchers as natural supinators. 

Although a natural supinator may struggle to generate backspin on the baseball, they often succeed by maximizing the east-to-west movement profiles of their pitches. Junis is no different. He rarely threw his sinker during his time with the Royals, but in the small sample we have, we can see that he generated approximately 15 inches of run on the pitch. This allowed him to get nearly 30 inches of horizontal movement differential between his sinker and his slider. Kansas City’s issue was not the development of the sinker; Junis had the pitch in his arsenal. They merely failed to recognize that embracing his supination-based throwing style was the key to his success. 

This is the part of the story where the protagonist enters the picture. In Junis’ story, the protagonist was the San Francisco Giants. Jakob Junis signed a one-year, $1.5 million contract with the Giants this past offseason. For the Giants, this was a low-cost upside play on a pitcher for whom they strove to develop. For Junis, this was a chance to play Major League Baseball and work with one of the most analytically-driven franchises with a proven track record of exceptional pitcher development. 

Analytics is a complicated field. The public’s perception of analytics is likely fueled by Peter Brand’s role in Moneyball as a Yale quant whose mathematical approach to the sport helped lead the 2002 Oakland Athletics to 103 wins. The brutal reality is that analytics can get a lot more complicated than that. Nowadays, professional teams employ ever-expanding data science departments that focus on predictive modeling with player tracking data to fuel player evaluation and player development. However, Junis’ rise from fringe big leaguer to productive front-of-the-rotation pitcher can be summarized by a piece of advice that may appear obvious to most. 

“Throw your best pitches more” 

You may be thinking “well… duh!” And I don’t blame you! It sounds like a rudimentary recommendation that should not even need to be said. Yet it does. Until baseball rids itself of the old-school mindsets that plague pitching, this simple piece of advice can serve as a competitive advantage for the more open-minded organizations, such as the San Francisco Giants. 

The Giants completely reshaped Junis’ pitch distribution. In 2021, he threw his slider 40% of the time, his fastball 35% of the time, his cutter 17% of the time, his sinker 4% of the time, and his changeup 3% of the time. Approximately halfway into his 2022 campaign with the Giants, distribution now sits at 53% slider, 32% sinker, 14% changeup, and 1% cutter. Through 709 pitches, Statcast has only tracked 5 four-seam fastballs from Junis.  

As you could have probably predicted, Junis’ optimized arsenal has led to massive boosts in production. At the 2022 All-Star Break, Junis has thrown 50 innings, while posting a 2.98 ERA, 1.01 WHIP, and 3.73 xFIP. Even though his swing-and-miss numbers have not changed much, the demise of his four-seamer has completely augmented his ability to limit hard contact. Junis has posted a considerable drop in Barrel%, HardHit%, wOBACON, and SweetSpot%. It has been a breakout season for Junis, and the Giants have been handsomely rewarded for their low-risk gamble on the 29-year-old righty who found himself in Triple-A a year ago. 

As hard as it may be to believe, this article isn’t really about Junis. Junis is merely a microcosm of a greater issue in baseball. Pitchers at all levels are constantly held back due to old-fashioned philosophies. Not everyone is cut out for a four-seamer. Not everyone needs to be a fastball-primary pitcher. It is perfectly fine to throw a slider over 50% of the time if it is far and away your best pitch. Just because there is a status quo on how to pitch does not mean one must follow that status quo. 

I would be lying if I said that these shortcomings in baseball philosophy aren’t diminishing. Fastball usage is decreasing every year in Major League Baseball and more-and-more pitchers are utilizing their best pitches as their primaries. Pitchers who struggle to generate backspin on the baseball are often shaping their arsenals around pitches that don’t require backspin, such as sinkers, sliders, and changeups. Regardless of the strides that the game has taken, Junis’ story demonstrates that there are still plenty of organizations that hold their pitchers back from maximizing their effectiveness. 

I am optimistic about the trends that we’ve seen in the tracking data era of baseball. Data is knowledge and knowledge is power. Well, let me rephrase. Knowledge is only power if it comes with the willingness to deviate from traditional viewpoints. Knowledge can only get a guy so far if they lack the willingness to utilize that knowledge.  

We do not know definitively if the Royals detected issues with Junis’ four-seamer, but it would be hard not to. After all, that pitch was as unproductive as his slider was productive. However, we do know that they failed to even scrape the surface of Junis’ potential due to their commitment to the heater that should have never existed in the first place. This isn’t a matter of placing Junis into a biomechanical laboratory to garner advanced reports on his mechanical composition. This is simply a matter of throwing your best pitches more—a piece of advice that seems so obvious yet evades the conventional wisdom that plagues pitching development.