Does Lost Fastball Velocity Come Back?
Hey everybody. Doing a little bit of SP research for the position breakdown series. In doing so, I ran into Shane Bieber who lost velocity on his fastball last year.
That made me wonder - does lost velocity one year mean it’s usually gone for good? I wanted to answer that question. The full answer is too long for a Twitter thread but not quite interesting or refined enough for a RotoBaller post, and I’m trying to be as quick as I can with it - so I’m doing it here.
The Study
We need three consecutive years of data to answer this question. We want to find pitchers that lost velocity from year 1 to year 2, and then see where their velocity was in year 3. We can’t do this with 2021 and 2022 because 2020 was a lost season.
So I went to 2016-2019 data to explore. What I did was find the list of all pitchers that lost at least 1.5 miles per hour on their four-seam fastball in a given year in that range, and then I looked at what happened the next year.
A lot of players were immediately eliminated because they didn’t throw at least 50 four-seamers in all three years, but we have enough results to matter.
In this sample, I found 49 players that lost at least 1.5mph of velocity one year and then threw enough fastballs the third year for us to check.
Of those 49, only four pitchers (8%) got their velocity back in the third year. I defined “got it back” by taking the first year and subtracting 0.2 miles per hour from it. If a pitcher goes from 94 to 93.8 - you wouldn’t really say he lost velocity, so I wanted to account for that.
If I am more gracious and say that “getting the velocity back” is getting with 0.5 mph of their first year, only seven pitchers show up (14%).
19 of the 49 pitchers (39%) saw their velocity decrease even further in the third year. Only three pitchers (6%) saw their year three velocity exceed their year one velocity.
If we compare year 3 with year 1, we see that the average change in velocity was -1.6 miles per hour.
If we compare year 2 with year 1, we see that on average pitchers lost 0.4 more mph on their fastball even after the big drop from year 1 to year 2.
It is not a pretty picture. The data is really telling us that the strong majority of velocity drops are for good.
Full data shown here, click on it for a better image:
Velo Losers
So who should this make us worry about? Here are the pitchers that lost at least 1.5 miles per hour of velocity from 2021 to 2022, ignoring the players that were in the bullpen in 2021 and then in the rotation in 2022 because that almost surely explains it, and it’s not a concern for us right now.
(SI means Sinker, FF means four-seam fastball)
Corey Kluber (SI): 90.7 → 88.9
Dylan Bundy (FF): 90.7 → 89.0
Kyle Freeland (SI) 91.3 -. 89.6
Michael Wacha (SI) 94.2 -. 92.6
Shane Bieber (FF) 92.8 -. 91.3
Well crap, there’s only one real fantasy-relevant name here. I guess I did all of this just to say that Bieber’s velocity is probably not coming back. But I learned something, and maybe so did you - thanks for reading!