Jack Leiter’s Fastball Exemplifies His Talent by Justin Choi April 6, 2021 This is Justin’s first piece as a FanGraphs contributor. Justin has always been a baseball fan and a writer, but it wasn’t until Hyun Jin Ryu began dominating in 2019 that he started to fuse those interests together. He’s written for a few places since then, including Prospects365 and Dodgers Digest, and is now hoping to pester the good people of FanGraphs with his deep-dives into niche topics. Outside of the baseball blogosphere, he’s a student at Washington University in St. Louis. Jack Leiter has been outstanding. So far this college baseball season, the sophomore from Vanderbilt University is sporting a minuscule 0.25 ERA in 36 innings pitched. He’s struck out 59 batters. Oh, and fun fact: He had a no-hit streak that lasted 20 innings. That’s largely thanks to a masterful no-hitter against South Carolina on March 21, during which he fanned 16 batters and allowed just a single walk. In his next start, he had seven no-hit innings going against Missouri but was pulled due to concerns over his ballooning pitch count. At this point, to call Leiter outstanding might even be an understatement. Of course, the ERA seems unsustainable, and it wouldn’t be surprising if the right-hander runs into a bad day – it’s a volatile sport, after all. But regardless of what happens in the future, he’s already made a lasting impression on fans and scouts. In the months leading up to the college baseball season, however, Leiter was at times overshadowed by teammate and fellow pitcher Kumar Rocker. And though Leiter was obviously well-regarded, his placement on public draft boards ranged. He was (and still is) No. 1 on our draft board, while MLB.com placed Rocker first and Leiter sixth in a ranking published in mid-December and Prospects Live featured Rocker first and Leiter fifth in their own mock draft published in January. Kiley McDaniel had Leiter second on his February board, ahead of Rocker, and noted that ranking Leiter above Rocker is “the consensus view after they’ve each made their first start of the season.” There’s no doubt that Jack Leiter is good. However, it can be tricky to evaluate him because some of the standard metrics undersell his greatness. For example, let’s consider his four-seam fastball. It averaged around 92 mph last season, a mark that hardly stood out. He’s bumped it up to 93-94 mph this season, and he does top out at 98, but it’s possible to have overlooked him in favor of more eye-catching flamethrowers. His raw spin rates are between 2200 and 2400 rpm, a range that would appear light-blue if displayed on a Baseball Savant page. You might have expected more from a top pitching prospect, and that’s understandable. This is where a relatively new metric called Vertical Approach Angle (VAA) comes to the rescue. You might already be familiar with it if you’ve read this great Alex Chamberlain article. He provides a more detailed explanation, but basically, VAA describes the angle at which a pitch crosses home plate. Some pertinent details: since pitchers throw from an elevated mound, VAA will always be negative, and it can be either flat (less negative), or steep (more negative). That’s it! In a world of baseball formulas that exceed our puny digit spans, VAA is not only intuitive but also easy to internalize. So why does it matter? VAA dictates where a fastball should be located in order to increase its efficacy, both in terms of generating whiffs and limiting hard contact. In general, fastballs with flatter VAAs thrive up in the zone, while fastballs with steeper VAAs thrive down in the zone. I should note, however, that unless a pitch’s VAA is extreme, it doesn’t seem to have a significant impact. Fortunately, Leiter’s fastball is an outlier. If we average out his VAAs recorded at the top, middle, and bottom areas of the zone from TrackMan data I’ve sourced, we get -3.6 degrees. That’s elite, even by major-league standards. As proof, here’s a list of the 10 flattest fastballs of the 2020 season, featuring Leiter: 2020’s Flattest Fastballs ft. Jack Leiter Name Pitches VAA Freddy Peralta 364 -3.6 Jack Leiter 328 -3.6 Edwin Díaz 214 -3.8 Lucas Sims 223 -3.9 Jacob deGrom 510 -4 Gerrit Cole 635 -4.1 Trevor Bauer 475 -4.1 Deivi García 317 -4.1 Mychal Givens 254 -4.1 Cristian Javier 560 -4.2 SOURCE: Alex Chamberlain’s Pitch Leaderboard For what it’s worth, TrackMan data on college players can sometimes be unreliable. Different schools have different measuring devices, all of which have varying degrees of accuracy. It could be that the data I’ve obtained is notably wrong. Not to mention that, as of now, we can only estimate the VAAs of major league pitchers. None of this really matters, though. What matters is that Leiter is somehow able to appear in the above table as a college pitcher. Some prospects take years of toiling in the minors to develop qualities present in established players, but in Leiter’s case, he’s armed with one at the age of just 20. Once you realize how flat the pitch is, it becomes impossible to ignore. I mean, take a look at this: I don’t care what the physics says – that pitch traveled in a straight, horizontal line. It’s as if someone drew its trajectory using a ruler and a pencil. As a batter, it must be frustrating to experience a fastball that keeps on going, going, and going, sailing right above where you expect to make contact. That doesn’t mean Leiter has to pitch exclusively up in the zone. In his article I mentioned earlier, Chamberlain discovered that while flat fastballs don’t generate whiffs when located down, they are still useful at eliciting called strikes there. Does Leiter exploit this fact, and do I have a GIF as an example? Yes, and yes: It’s against a college crop of hitters, sure, and better, pro hitters might not be quite as flummoxed, but the point that an extreme VAA comes in handy irrespective of vertical location still stands. What’s his secret? The answer lies in his release height, a variable that alters VAA. For example, if other things are held equal, a pitch from Josh Hader (low release point) will generate a flatter VAA than one from Blake Snell (high release point). Mentally picture their throwing motions, and the idea should make sense. Listed as 6-foot-1 on the Commodores’ website, Jack Leiter is an unconventional pitching prospect. But he’s managed to transform a potential weakness into one of his greatest strengths. So far this season, Leiter has averaged a release height of 5.2 feet, allowing him to minimize the approach angle of his fastball. In addition to a low release height, Leiter possesses elite extension, which measures how far a pitch is released from the mound. Longer extension often leads to a lower release height and thus a flatter VAA, which helps, but the real benefit lies in how it affects perceived velocity. Earlier, I mentioned that Leiter is averaging 93 to 94 mph on his fastball. In reality, it’s likely that the speed opposing batters experience is a tick or two above what radar guns would tell you, giving Leiter a competitive edge. To demonstrate this effect, I compiled major league pitchers in 2020 who threw at least 100 fastballs. I then plotted their average extension on the x-axis, and the difference between their release speed and effective (perceived) speed on the y-axis. The difference represents the velocity pitchers “gain” from their extension. Lastly, to avoid messing up the axes, I’ve elected to only look at pitchers who had a positive difference. Here’s how all that looks, together: There’s a clear-cut correlation between extension and the difference in speed. Release the ball closer to home plate, make hitters’ lives worse. It’s nothing new, but does illustrate the benefits of extension, at least as it pertains to four-seam fastballs. It also, hopefully, illustrates why hitters have such a difficult time with Leiter. They have milliseconds to react to high-speed pitches. The fact that Leiter’s mechanics allow him to erase a good chunk of that precious time, combined with the added difficulty of dealing with a flat fastball, is ridiculous. Not even middling raw spin rates have been an issue for Leiter. That’s because his fastball’s spin efficiency – the percent of a pitch’s spin that contributes to its movement – is regularly above 95%. Spin rate on a fastball doesn’t matter unless the spin is helping to defy the pull of gravity, and well, Leiter’s fastball is averaging nearly 20 inches of vertical break this season, according to TrackMan data I’ve collected. An added bonus: spin-efficient fastballs perform well up in the zone, a fact that pairs well with Leiter’s aforementioned characteristics. Putting it all together, it’s time for a fun activity: comps! We’ve explored several metrics, like VAA, extension, spin efficiency, and vertical break in order to wax poetic about Leiter’s fastball. The important question, though, is how those metrics compare to those of notable pitchers. Let’s have a look at our contestants: Jack Leiter vs. the World Name VAA Extension (ft) Rel. Height (ft) Spin Eff. (Active Spin) VB (in.) Deivi García -4.1 6.6 5.3 98% 18.6 Gerrit Cole -4.1 6.6 5.6 98% 17.9 Jack Leiter -3.6 6.6 5.2 >95% 19.9 Josh Hader -3.6 6.8 5.2 97% 17.1 Shane Bieber -4.5 6.6 5.7 98% 18.3 Trevor Bauer -4.1 6.5 5.6 94% 19.9 SOURCE: Alex Chamberlain’s Pitch Leaderboard What surprised me is how difficult it was to find pitchers with fastballs similar to Leiter’s. The list grew thin after the obvious choices of Gerrit Cole, Shane Bieber, and Trevor Bauer, which is why I had to stretch it out with Deivi García. This speaks volumes about Leiter’s talent, but also, reveals that the combination of low release height, huge extension, and high spin efficiency is still a relatively new idea in the world of baseball. His set of skills is, at the moment, special. By the time he’s ready to make his major league debut, though, it wouldn’t surprise me if dozens like him emerge. Analytically-savvy organizations like the Dodgers, Rays, and Reds have hopped on the bandwagon, and it’s only a matter of time before others catch up. Beyond the fastball, Jack Leiter throws a curveball that complements it with a mirroring spin axis. His slider and changeup are also solid offerings. In sum, Jack Leiter is the ideal modern pitching prospect, one who encapsulates the direction in which player development is headed. He does need to demonstrate that he can wield his flat fastball against higher levels of competition for us to crown him a potential ace, and I should note that I’m not making a direct comparison between the entirety of the pitchers I named above and Leiter, because that would be silly; it’s just their fastballs that are relevant. But those caveats aside, Leiter’s dominance is no fluke. As the college baseball season chugs along, I’d recommend keeping a close eye on his performance and evolution as a pitcher.