PicoBlog

In 2018, Clayton Kershaw’s fastball velocity declined, down to 90-91 MPH. Since then, it’s fluctuated a little bit, but has essentially remained in the same band. In that time, he’s been almost as dominant as his early days, striking out 9.5/9 IP, with a 27% K% and a 22.1% K-BB%, for an ERA of 3.10 and a FIP of 3.23.

Cristian Javier last season struck out 33.2% of the batters he faced, powered by a fastball that averaged “only” 93.9 mph. Paul Sewald has been dominant with a 92.5 mph fastball.

Classically, we think of the primary metric for the fastball as the velocity band, along with the “max”. It’s typically the first thing you read about with a prospect. In fact, just yesterday, MLB Pipeline posted this: Prospects With The Best Fastballs, which is mostly just the guy who throws the hardest in each org. Guillermo Zuñiga might have a sexier fastball than Cooper Hjerpe, but is it actually better?

Andres Munoz last season averaged over 100 mph with his fastball. FanGraphs had it has 1.52 runs below average despite him using 35% of the time. His slider was amazing, of course.

I think the first thing we should be talking about with a pitcher, is their fastball shape, and then, if they have good shape, do they also combine that with elite velocity?

Let me show you four pictures:

Red = better for the pitcher, blue = better for the batter.

This is the same picture, but rotated. It’s clear that Induced Vertical Break (IVB) is the primary drive of value, rather than velocity.

IVB/S is a metric that takes into account that harder fastballs have less time to rise, so it will give credit to those pitchers with great extension and velocity, or rather, not penalize them for having less time to induce vertical break.

We see that pretty much any four seam fastball with at least 42 inches IVB/S is a good fastball, even the “slow” 88-89 mph ones.

Technical Note: The totals don’t match since it’s filtering buckets to a minimum of 500 pitches, so the samples are slightly different.

This comparison chart explains why I believe IVB/S is (slightly) preferred to IVB. Scan down the IVB chart (the one on the bottom) for the 18" inch bucket. This tells you that 18 inches of induced vertical break is great, but only if your fastball is above 92-93 MPH. If you can cross the 20” threshold, it’s dynamite.

If we look at IVB/S, we can see that no matter the velocity, if you can get 44” of IVB/S, you’ll have an above average fastball, almost at any speed and a very linear effect as you increase.

Andres Munoz averaged 4.8” of IVB and 35.1” of IVB/S, which is why his fastball wasn’t that good. It *feels* like his fastball should be a dominant pitch, but even a 100 mph fastball with mediocre shape, is hittable.

If you can get to 50” of IVB/S you have an elite fastball. If you can get close to 56, you’re basically unhittable. With velocity, the effect is real, but much more muted:

Here’s 2022 pitchers sorted by IVB/S:

Same list, but just starting pitchers:

Velocity matters (despite the click-bait headline). The main takeaway here is that rise (as measured by IVB/S) matters much, much more. If we’re evaluating pitchers based on their fastball, I’d much rather know what their IVB/S is, than how hard they throw. If you want to know which pitchers will be overrated by Stuff models, it’s probably the pitchers like Pivetta and Urquidy who are great by this metric, but otherwise don’t have the performance we’d expect given the fastball shape.

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