What Happens the Year After a Velocity Spike?

I didn’t want to write this article. One of my favorite things to do, back when I was a full-time Cardinals fan and part-time writer, was wait for the first few weeks of the season and then start ogling velocity changes. There’s almost nothing that made me feel so unabashedly happy as seeing an extra tick or two out of some arm I’d written off the previous year. Why spoil that magic by looking into whether it actually matters?

Nothing fun can come of using data to look at incuriously held beliefs, but that’s never stopped me before, so I decided to examine pitchers who experienced velocity gains from one year to the next. Do their fastballs grade out better? Do they strike out more batters? Walk more? Do they hold the gains from one year to the next? I had no clue, but I decided to find out.

First things first: 2020 goes right out the window. The season started in late July, and no one had anything approaching their normal offseason routine. Temperatures were weird, workloads were changed on the fly, and some teams were affected by COVID-related cancelations; trying to tease something out from that noise is pointless and unnecessary. I’ll just use 2015 through 2019 instead.

Why 2015? That’s when Statcast first arrived, and with it a new tracking system. I could, I suppose, use data since 2008, but I wanted to minimize the chances of false readings stemming from the change in systems. 2020 also featured a change — to camera-based readings instead of radar — but we’re already throwing it out anyway, so no big deal there.

In each year, I looked at the population of starters who threw at least 500 four-seam fastballs. I then found the year-to-year changes for each pitcher-season combination. Justin Verlander, as an example, averaged 93.4 mph in 2015, 94.1 mph in 2016, 95.3 mph in 2017, 95 mph in 2018, and 94.6 mph in 2019. That means his ‘15-’16 change was 0.7 mph, his ‘16-’17 change was 1.2 mph, his ‘17-’18 change was -0.3 mph, and his ‘18-’19 change was -0.4 mph. This gave us a database of 236 pitcher-seasons from 2016 to 2018 — I’m leaving out changes between 2018 and 2019 because I want to know what happens the year after a pitcher gains velocity.

Aside from requiring the fastballs to be thrown as a starting pitcher, I was completely context-agnostic. Verlander was recovering from injury; someone with similar velocity gains might have gone to Driveline in the offseason or just have been a young pitcher who got bigger and stronger. I’m not trying to be a pitching development coach — there are plenty of those out there already, and they’re doing a great job. I’m merely asking a question from the outside: if you, the fan, see a pitcher throw harder, what should you expect?

We’ll focus on the extreme gainers for this study, because I’m not very interested in what becomes of pitchers who averaged 93.1 mph one year and 93.2 mph the next. There were 23 seasons where a pitcher increased their average velocity by a tick or more from year-to-year. No pitcher showed up more than once, and the group ran the gamut from fireballers like James Paxton (94.9 mph in 2015, 97.5 mph in 2016) to Kyle Hendricks types like, well, Kyle Hendricks (86 mph in 2017, 87.3 mph in 2018).

My first question for this exclusive group of gainers was whether they used their fastballs more. They didn’t, though that’s more a matter of league trends than anything else. On average, their four-seamer usage dropped by 1.3 percentage points, a rounding error away from unchanged.

By pretty much every value metric, however, adding velocity paid off. Strikeout rates improved by 2.5 percentage points, and the median was even higher at 3.1 percentage points. Walk rates fell by 0.4 percentage points (median -0.3 percentage points). Pitch values increased, even taking into account Chris Young’s disastrous 2016 — by an average of 0.17 runs per 100 pitches (median of 0.46 runs per 100 pitches). Take a look at each pitcher’s year-to-year change in each category I considered:

While that isn’t a surprising result, it is a gratifying one. Pitchers who add velocity to their fastball do better with it — pitch values take everything into account, from a taken strike to a home run. That’s a great sanity check, because it means our natural excitement at a velocity spike makes sense. If you see a pitcher on your team throwing harder, congratulations — he’s probably better now.

If that was all I had to tell you, I probably wouldn’t write this article. Never say never — it’s December 21, which means finding new and interesting things to say about baseball isn’t exactly a breeze. Luckily, however, I’ve got slightly more than “throwing your fastball harder is good.” Remember, that we don’t have to stop at two years. We can add an extra year, because we’ve set aside 2019 data specifically to answer what happens in Year Three.

First, let’s set a baseline. There are 158 instances of a pitcher throwing at least 500 four-seamers in three consecutive years in our database. As you might expect, they lost velocity, on average, from year to year. More specifically, they lost 0.21 mph from Year 2 to Year 3, though the same anomalous 2019 velocity bump I’ve found in other research was visible here as well.

How did our group of velocity gainers do the year after its big increases? The guys who threw in three straight years were indistinguishable from the pack. More specifically, they lost 0.32 mph on average. That’s statistically indistinguishable from the larger group’s performance, which is a great sign for those pitchers. That means that a velocity bump doesn’t automatically fade away the next year, which I feared might happen.

That leads me to the question I was pondering all along: what happens to pitchers the year after they see a velo pop? I looked at the same changes — pitch value per 100 pitches, strikeout rate, and walk rate — to see whether pitchers held their gains in subsequent years.

Conveniently enough for the narrative you no doubt had in your head, it seems that pitchers mostly held their gains. We’re looking at minuscule sample sizes at this point — only 16 pitchers worth of data — but there’s almost nothing to speak of. Fastball pitch values were essentially unchanged. Strikeout rate ticked up ever so slightly, by less than one percentage point. Walk rate also went up, though by even less — roughly 0.2 percentage points. In other words, what you saw when their velocity ticked up is mostly what you got the next year.

I don’t want to make too much of this finding, because the methodology is bare-bones and the sample size is tiny. With that caveat, I feel fine saying that the way we all think about velocity gains seems basically correct. If a pitcher starts throwing a faster fastball, that fastball is better. The pitcher gets better, too — in both walk rate and strikeout rate. Sometimes it’s as simple as it seems — if your favorite pitcher starts throwing harder, good times will follow.