That is Michael Rosen’s first piece as a FanGraphs contributor. You might have learn his earlier work on the website, together with his article concerning the Kirby Index, a metric he created to measure command utilizing launch angles. He lives in Los Angeles and works as a transportation planner.
Earlier this yr, I attempted to resolve the riddle of how Shota Imanaga threw his invisible fastball. The pitch had (and nonetheless has) a uncommon mixture of traits: On the time of writing, solely Imanaga and Cristian Javier threw fastballs from tremendous flat vertical strategy angles (VAA) with elite induced vertical break (IVB). A fastball with a flat VAA or excessive IVB performs a trick on the hitter’s notion; a fastball with each qualities turns into practically unhittable, or invisible, when positioned on the prime of the zone. I posed two questions in that piece: Why was this invisible fastball so uncommon? And what was Imanaga particularly doing to throw a fastball with these traits?
The primary query will be answered, my analysis reveals, by wanting instantly at launch angles. Launch angles replicate the path that the pitcher is aiming the ball at launch, which I wrote about at size in my article on the Kirby Index from Might. That act of aiming — particularly, the path the ball is oriented out of the pitcher’s hand — additionally impacts the quantity of backspin on a four-seam fastball.
The plot beneath reveals the connection between backspin (measured as x-axis spin) and vertical launch angle for four-seam fastballs through the 2024 season by way of August 5. The plot captures the linear relationship between the 2 variables. As the discharge angle flattens, the quantity of backspin drops:
Fastballs resist gravity — in different phrases, they’ve extra IVB — when they’re thrown with extra backspin. They basically trick the batter into pondering that the pitch is rising. In consequence, batters are inclined to swing beneath pitches with numerous backspin, leading to a rise in each whiffs (misses) and innocent fly balls from contact made beneath the ball.
When a pitcher releases a fastball from a steeper vertical launch angle — in different phrases, when the ball is pointed extra towards the bottom — it permits the pitcher to get “behind the ball,” creating the carry or journey impact that IVB measures. When the pitch is launched at a flatter vertical launch angle, it’s harder for the pitcher to backspin the ball.
Riley McCauley, a former minor league pitcher who now works as a coach within the Phillies’ system, defined why a pitch with a steeper launch angle would generate extra backspin.
“The upper the slot is, the extra behind the ball, the decrease the vertical launch angle is, usually the higher alternative you most likely must backspin the ball,” McCauley informed me.
This relationship between fastball backspin and launch angle flatness explains why there’s an inherent tradeoff between VAA and IVB. Throwing a fastball from a flatter (and due to this fact extra advantageous) launch angle typically ends in a concurrent sacrifice of IVB.
Imanaga, alternatively, throws his fastball excessive within the zone with comparatively flat launch angles and nonetheless manages to provide elite carry. This leads into my second query: How is he doing this?
The reply seems to boil right down to outlier mechanical expertise. Not solely is Imanaga a Kirby Index king — top-of-the-line pitchers within the league at repeating his launch angles — he’s additionally able to throwing a fastball that optimizes for swing-and-miss like virtually no different pitcher. Each these expertise will be understood, ultimately, in relation to his launch angles.
Measuring these mechanical expertise, as I wrote in my Kirby Index article, is the following frontier of baseball evaluation. However essentially the most subtle evaluation won’t be carried out by the general public — it should occur in massive league entrance places of work, with groups deploying dozens of analysts to parse the outputs supplied by corporations like KinaTrax, who observe each single a part of a pitcher’s physique because it goes by way of the pitching supply.
Launch place was our first trace of the affect of mechanics on spin; launch angles get even nearer. Additional down the rabbit gap, there will probably be variables like hand place, finger strain, wrist motion, arm pace, and different mechanical influences. Driveline Baseball, by way of their OpenBiomechanics Venture, is giving the general public a way of what sort of information groups might need at their disposal. (Their Github documentation has an excellent rundown of the particular variables which can be measured with movement seize information.)
To grasp why Imanaga throws an excellent fastball, it’s obligatory to take a look at the biomechanical parts of his supply. Evaluation of those parts could nicely open up the following information benefit for groups. As Eric Longenhagen wrote in his 2024 draft recap, quoting a member of a entrance workplace: “We’re all making choices wanting on the similar information and, more and more, primarily based on related interpretations of that information.” Biomechanical information might permit groups to distinguish themselves as soon as once more, constructing biomechanical fashions that may spot the following Imanaga after a single pitch. Launch angles are on the threshold of all of this, however behind the biomechanical curtain, entire worlds of modeling prospects exist. Behind the scenes, the arms race is on.
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4 forces act on a spinning four-seam fastball in flight. The Magnus power follows the path of the pitcher’s fingertips, pushing within the path that the entrance of the ball is shifting. Gravity drags the ball towards the bottom at roughly 32 toes per second squared. Seam-shifted wake sends the ball in unpredictable instructions if the ball’s spin orientation is uneven. Drag goes in the wrong way as ball flight, slowing it down because it approaches house plate.
For a four-seam fastball, the Magnus power is chargeable for the widespread phenomenon that we describe as journey, hop, and carry. It’s generally measured utilizing IVB or drop. If a ball spins extra, it stays up longer, resisting the pull of gravity.
I needed to research which mechanical components affect fastball carry. What’s the pitcher particularly doing to create stick with it the fastball?
Launch top is one biomechanical variable recognized to narrate strongly to fastball carry. The connection between launch top and fastball carry is nicely documented, to the purpose that sensible analysts like Alex Chamberlain have identified {that a} pitcher’s carry have to be understood throughout the context of their launch top. The logic goes that hitters anticipate a sure carry from a given launch top due to the tight relationship between these two variables.
I needed to discover the opposite components that permit pitchers to generate carry. Sure, fastball carry is a perform of backspin, however which components permit for optimum backspin on the pitch?
(A fast methodological apart: There are a number of methods to judge the carry of a fastball. The 2 most typical methods are IVB and drop. Each of those variables are influenced by the speed of the pitch towards house plate. Slower fastballs get a lift in IVB; sooner fastballs are rewarded by drop merely for being quick. If we’re primarily within the particular carry traits of a given fastball, it makes essentially the most sense to look particularly at its vertical acceleration, or “az” in Statcast parlance, from which each IVB and drop are derived. Az is measured in toes of drop per second per second, so a pitch that drops precisely with gravity would have an az of -32.)
It seems that a fastball’s vertical launch angle is a significant factor. I cooked up a linear regression with 5 impartial variables: pitch location, vertical launch angle, velocity, launch top, and launch extension. The regression defined 99% of the variation in fastball carry; when the variables have been unit normalized, vertical strategy angle had the strongest impact dimension, even stronger than launch top:
When the pitch is launched from a steeper angle — in different phrases, when the pitch is aimed extra downward, with a higher preliminary vertical velocity — it generates extra carry. When a pitch has a flatter goal, or a launch angle nearer to zero levels, it generates much less carry. Here’s a plot of each four-seam fastball thrown within the 2023 season, with launch angle on the x-axis and vertical acceleration on the y-axis. You’ll be able to see that as the discharge angle flattens out, the pitch drops extra with gravity:
The connection is even stronger when averaging outcomes on the particular person pitcher stage. Beneath is a plot of the typical vertical launch angle of every beginning pitcher plotted towards their fastball carry:
One may suppose that the connection between launch angle and carry is mediated by arm angle and launch top, however this doesn’t seem like the case. Even inside a given pitcher — and due to this fact holding arm angles and launch heights comparatively fixed — this relationship holds up. The typical R-squared of within-pitcher launch angle to acceleration for four-seam fastballs sits at about 0.2. Right here’s Miles Mikolas, for instance:
The connection of launch angles to each location and fastball carry explains why there isn’t any obvious relationship between fastball carry and site. Contemplate this plot of all four-seam fastballs by way of July 4:
On the x-axis is vertical acceleration; on the y-axis is the placement of the pitch. It appears like there’s no relationship between the carry of a fastball and the place it crosses house plate vertically, proper? Not so quick.
Right here’s the identical plot, besides this time with every pitch coloured in as a perform of its vertical launch angle:
It seems there’s a relationship between fastball carry and site — it’s simply mediated by the discharge angle.
The blob illuminates the varied ways in which a pitch can find yourself excessive within the zone. It may be thrown with a flat launch angle and virtually no carry, or it may be thrown with a steeper launch angle and extra gravity-resisting backspin. They’re completely different paths to the identical location.
I emailed Dr. Alan Nathan about this, and he provided his concept for the connection between fastball carry and launch angles.
“If the preliminary path is just too steeply downward, then the ball may find yourself beneath the underside of the zone,” Nathan wrote. “That may be countered with backspin. So I’m guessing that the steeper the downward launch angle, the extra backspin is required to maintain the ball within the strike zone, which implies a decrease [vertical acceleration].”
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A number of readers of my Kirby Index article expressed skepticism that the metric revealed novel insights about pitcher command. In any case, launch angles are calculated as a perform of 9 parameters which were accessible for the reason that creation of PITCHf/x. Researchers like Scott Powers and Stephen Sutton-Brown have leveraged these 9 parameters to push command modeling to the leading edge; if there was juice to squeeze right here, these fashions could be squeezing it.
What a minimum of one reader prompt is that if the general public had entry to biomechanical launch angle information — not simply launch angles derived from preliminary attributes like velocities and accelerations — these information might result in promising insights. Whereas the general public could not have entry to this biomechanical information, main league groups do, whether or not it’s by way of third-party suppliers like KinaTrax, or by way of information supplied instantly by MLB by way of Hawk-Eye Professional in partnership with Reboot Movement. And launch angles are simply the tip of the iceberg.
If command and stuff are downstream of launch angles, then launch angles are downstream of processes even additional again within the supply. McCauley, the Phillies coach, defined how all of those variables join.
“I feel quite a lot of instances we do take a look at the wrists and the discharge level, however I feel the decrease half happening the mountain units that up,” McCauley informed me. “I feel guys like [Justin] Verlander and [Tyler] Glasnow have fairly upright, linear decrease halves, whereas guys like Josiah Grey and Joe Ryan have these low, slingy slots with tons of VAA [and] are usually form of crossfire [with] very rotational decrease halves. The decrease half units up what occurs with the remainder of the supply, and the supply impacts ball flight on the similar time.”
KinaTrax is likely one of the most outstanding suppliers of biomechanical information. They got here on the scene practically a decade in the past when the Tampa Bay Rays put in their software program at Tropicana Area. In response to Scott Coleman, the director of biomechanics at KinaTrax, the corporate took a significant step ahead following the 2020 season once they realized the benefit of amassing markerless movement seize information.
Utilizing their improved expertise, KinaTrax might prepare their cameras on main league gamers and seize dozens of biomechanical variables alongside the way in which — not simply launch angles, however the pitcher’s exterior rotation, shoulder abduction, hip/shoulder separation, and dozens of different variables. Know-how like this makes it doable to measure every side of the kinematic chain intimately.
This biomechanical data — not simply launch angles, which have a powerful relationship to each command and stuff, however the whole lot downstream of those launch angles — can doubtlessly be leveraged to construct higher predictive fashions, figuring out hidden draft prospects, recognizing accidents, and accelerating the participant growth revolution.
And in contrast to the older era of ball flight information, which principally each crew is equally able to using at this level, there seems to at present be a variety of experience with regards to implementing biomechanical insights. There are 20 groups that contract with KinaTrax, for instance, however not all of them have interaction with the information in the identical method.
“There are some groups on the market which have lots of people that deal with simply our information,” Coleman informed me. “After which there’s some groups which have, you already know, one or two folks.”
Again in 2022, Eno Sarris and Alec Lewis wrote about the way forward for biomechanics and pitching evaluation for The Athletic. In that story, they prompt that “one of many final frontiers for biomechanics will are available linking the way in which pitchers transfer to precise outcomes on the sphere.” The connection of launch angle to each command (the Kirby Index) and fastball carry reveals how pitching outcomes will be linked on to how pitchers transfer.
On the general public facet, launch angles, and their significance to quantifying each command and motion, level to the ability of biomechanical variables in explaining pitcher high quality. However the true analysis is happening behind closed doorways, utilizing terabytes of complicated biomechanical information to unearth the following nice pitcher.
Each crew has a “stuff” mannequin, and people fashions doubtless all look fairly related at this level. However modeling pitcher efficiency primarily based on biomechanical inputs — that’s the place the following data asymmetry might emerge. Maybe it already has.
