Friday, September 22, 2023
Heaters by Movement
Suppose we want to tag a pitch when it's at least 3 mph above the league average. That seems too simple to do right? The league average fastball is 94 mph, so tag any fastball that is 97+. Case-closed. Or not?
Not. I did say pitch, not fastball. Ok, so then we look at league-average speed of sliders, and repeat. Rinse and repeat with cutters and curves and so on. Case-closed? No. A slider is not a slider for everyone. There is in fact an infinite number of classifications for a pitch: every pitch is as unique as a snowflake. That we've tried to compartmentalize them into a dozen groups does not mean that those groups are clear and distinct. You can have two pitches, same speed, same movement, and one would be called a slider, and another a curve. That's the reality that we live in.
Let me show you something cool. Well, cool for me, and if you are here, presumably it's going to look cool to you. This is the average pitch speed of ALL(*) pitches, based on their movement profile.
(*) See at the end where I talk about changeups.
So, a pitch that has backspin and tails arm-side, those average 94 mph. While those are typically fastballs, they could be cutters too. A pitch that has topspin and hooks glove-side, those average under 80 mph. While those are typically curves, they could be sliders too. The main point: we don't care what they are called, we just care how they move. And having established how they move, we simply figure out the average pitch speed of those pitches.
Now that we have the average speed of a pitch based on their movement (rather than some overarching pitch type), we can evaluate each single pitch, one at a time. We determine the movement profile on a pitch by pitch basis, look up the average speed for such a pitch, and compare it to the actual pitch speed thrown by that pitcher on that pitch. If the actual speed is 3+ above that baseline, great, we'll tag that pitch as being hot.
Let's look at all those pitches that were classified as four-seam fastball since 2020, and see how often each pitcher threw a hot pitch. (Click to embiggen) It should surprise no one that 100% of Jhoan Duran's fastballs were hot. You will see a bunch of familiar names. Plus Garrett Richards. Now, how does someone who averages 94-95 mph on their fastball end up with over 90% of those pitches being hot? Well, Garrett Richards may have these pitches classified as fastballs, but they could just as well be cutters. His fastball is thrown with a tremendous amount of gyro action, and so, it ends up being a cusp pitch. This is a good exception of what happens when you compartmentalize things. But in our Heater process here, it's irrelevant: all we care about is how it moves. And based on how the pitch moves, the MLB average pitch speed for that movement is 89.4 mph. And so, his fastball being 94.5 mph will end up being hot fairly often. And in this case, it's over 90%.
We can look at any other pitch type as well. Let's look at cutters. And here we can see a reverse-issue with David Robertson: while we call his pitch a cutter, and it would seem it's pretty high pitch speed at 93mph for a cutter, it's not a hot cutter, as he almost never gets above the threshold. And that's because the movement profile of his cutter is closer to a four-seamer. When we come to these cusp pitches, and we have to choose one and only one pitch type, we are basically stuck. Robertson is a cutter that moves more like a fastball (left image), Richards is a fastball that moves more like a cutter (right image). But, it's irrelevant for what we are doing here.
The top Heaters in 2023:
- +10 Clase (Cutter, hot 100% of the time)
- +8 Duran (4-seamer, 100% hot)
- +8 Kelly (Curve, 99% hot)
- +8 Ashcroft (Cutter, 99% hot)
- +7 Kelly (Slider, 99% hot)
- +7 Aroldis (Sinker, 99% hot)
- +7 Ben Joyce (4-seamer, 100% hot)
(*) So, changeups. They are problematic. For the moment, I've accepted the classifications for changeups, splitters, forkball, and screwballs, and removed all those pitches from everything I did above. I should do something more objective, but for now, this will do. I will note that changeup speeds are not based on their movement profile. And so, how a changeup moves doesn't really matter in terms of whether a changeup is hot or not. Even the very idea of a hot changeup seems odd to begin with. In any case, just pointing out that these pitches are problematic, and I'll get back to it later.
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