Velocity Changes During the 2018 Season

It may seem that fastball velocity gets over utilized for explaining a pitcher performance, but I don’t think it gets used enough. As I get going full steam ahead in my off-season research, I find myself always looking to see how a pitcher’s velocity held up over the season. Instead of looking up each pitcher individually, I decided to go ahead and collect 2018 fastball velocity reading for an easy reference.

For the data, I found the pitcher’s velocity for the whole season, April to June, July to October, and just September/October. The entire data dataset can be found here.

I went through the data and found some intriguing pitchers who gained and lost a few ticks. I divided up the analysis between first versus second half and first half and September. Many of the same pitchers would have made both lists. Here is the first to second half values.

Notable 1H to 2H Fastball Velocity Changes
2Hv-1Hv Pitcher Fastball Count Season Velo 1H Velo 2H Velo Sept Velo
-1.7 Stephen Strasburg FF 996 94.6 95.3 93.6 93.3
-1.2 Dereck Rodriguez FF 710 91.6 92.4 91.2 90.9
-1.1 Marco Estrada FF 1230 88.5 89.0 87.8 88.0
-1.0 Antonio Senzatela FF 976 93.6 94.4 93.4 93.1
-0.9 Tyler Skaggs FF 931 91.5 91.8 90.9 90.0
-0.9 Brad Keller FF 992 94.3 94.9 94.0 94.3
-0.8 Marco Gonzales SI 650 90.1 90.4 89.6 89.3
-0.8 Jon Gray FF 1387 94.7 95.0 94.3 94.2
1.1 Zack Wheeler FF 1295 95.8 95.3 96.4 95.8
1.1 Mike Clevinger FF 1735 93.6 93.0 94.2 94.5
1.2 Gerrit Cole FF 1617 96.2 95.6 96.7 96.5
1.2 Jacob deGrom FF 1399 96.0 95.4 96.7 96.9
1.3 Jordan Hicks SI 707 100.5 99.7 101.0 101.1
1.4 Cole Hamels FT 450 91.4 90.8 92.2 91.8
1.5 Gio Gonzalez FF 885 89.8 89.0 90.5 90.3
1.5 Lucas Giolito FF 1305 92.3 91.7 93.2 92.5
2.2 Matthew Boyd FF 904 90.4 89.3 91.5 92.4

Stephen Strasburg is the most concerning name on the list with his fastball down ~2 mph. The drop occurred after he went on the DL with shoulder inflammation.

His results also took a hit with his ERA going from 3.46 to 4.20 and his K%-BB% dropping from 23% to 19%.

Strasburg is getting in the danger zone where his fastball will start losing its effectiveness if he loses any more velocity. Here are its swinging-strike rates since he joined the league at different velocities.

Strasburg’s Fastball Swinging-Strike Rate
mph SwStr%
92 4.8%
93 7.0%
94 12.7%
95 13.9%
96 16.8%
97 14.7%
98 16.0%

The fastball starts to lose its effectiveness as it dips near 93 mph.

With the velocity drop, Strasburg will still be a good pitcher because his changeup is elite and curve and slider are decent. His issue is that he’s already been cutting his fastball usage from 73% when he entered the league to 52% last season. I think the chances of him having that elite season has passed.

One major consideration will be if he can get his walks under control. In the first half, they were at 2.1 BB/9 but jumped to 3.5 BB/9 in the second half. Spring training reports are going to matter quite a bit on how he gets valued.

Notable 1H to September Fastball Velocity Changes
SEPv-1Hv Pitcher Fastball Count Season Velo 1H Velo 2H Velo Sept Velo
-2.2 Danny Duffy FF 1044 93.0 92.9 93.1 90.7
-2.1 Chris Sale FF 957 95.3 95.1 95.9 93.0
-1.6 Corey Kluber FC 922 88.5 88.7 88.3 87.0
-1.5 Aroldis Chapman FF 679 98.9 99.1 98.5 97.6
-1.3 Bartolo Colon FT 1369 86.9 86.9 86.8 85.6
1.4 Luis Castillo FF 944 95.9 95.5 96.4 96.9
1.5 Patrick Corbin FF 630 90.8 90.5 91.1 92.0
1.6 Tyson Ross FF 1226 90.7 90.4 91.1 92.1
1.8 Drew Pomeranz FF 576 89.4 88.9 89.9 90.8
1.9 Sean Newcomb FF 1833 92.9 92.7 93.3 94.5
2.0 Mike Fiers FF 1095 89.4 88.5 90.2 90.5
2.7 Martin Perez FT 703 92.5 91.4 92.9 94.1

Corey Kluber is the name which jumps off. For pitcher going in the second round of mock drafts, an ~1.5 mph drop in his fastball throws a major red flag.

He got hit around more in the second half with his BABIP jumping from .248 to .321 while list strikeout and walk rates remained constant (22.5 K%-BB% to 22.1 K%-BB%). Kluber found a way to be effective even with the velocity loss.

My gut says something is off but I can’t find it. His steamer projection has his ERA next season back in the 3.50 range (same as 2015). so it even sees that something is not right. I’ll read some more previews as the season nears and see if I can gain a better understanding of him.

We hoped you liked reading Velocity Changes During the 2018 Season by Jeff Zimmerman!

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Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won three FSWA Awards including on for his MASH series. In his first two seasons in Tout Wars, he's won the H2H league and mixed auction league. Follow him on Twitter @jeffwzimmerman.

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Good scratching of the surface. Some things I’d love to know: Relationship between loss of velocity from 1H to 2H and change in RA9 or FIP. Is there a linear relationship or does it depend on starting velocity? What about next year? What happens next year when pitchers lose or gain velocity from 1H to 2H (in velocity and RAo9 or FIP)? And what happens to pitchers next year when lose or gain velocity only in September ? Next article?


You should be his editor! I want all of these questions answered and will gladly click and read if there is a follow up!!