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. Read the rest of this entry »