Arm Angles and Induced Vertical Break

AA, VAA and VAAAA

A week ago or so, Alex Eisert was kind of enough to offer this suggestion:

Alex Eisert @Mind_OverBatter

@EliBenPorat It's hard to analyze Stephens looking at movement averages. The dude varies his arm angle pretty dramatically, leads to different movement. Have you been accounting for arm angle variation?

As a matter of fact, I was not thinking about arm angles at all. I had just assumed that it was impossible. Turns out, it’s actually pretty easy to calculate, just hop on over to Alex’ article and find the link showing you how to calculate it. While you’re on the site, also take the time to read another Alex’ article, where he talks about VAAAA (not a spelling error).

The Link Between Arm Angles and IVB

Sometimes, you poke around with data and something pops out at you. I’ve been doing baseball research for a while, and it’s quite rare to get this type of result. The last time I remember getting a surprising result was in 2018 when I discovered the link between standard deviation of launch angle and BABIP. Alex Chamberlain also independently discovered this in 2019 and talked about it here. Please don’t read the previous sentence as a passive-aggressive statement; I truly worry about the originality of everything that I do, and as a researcher, it’s next to impossible to know if someone, somewhere has already published something similar. If I’m covering ground here that someone has already published, please let me know so I can properly credit.

** IVB is heavily correlated to Arm Angles **
R2 = 0.4 (FF only, 2022, Min. 100 Pitches)

I tweeted out the above pic, which generated a lengthy discussion. Twitter makes it very difficult to follow threads, but somewhere in the tweet thread, Alex (of the Chamberlains) mentioned that this is probably related to VAA or VAAAA (see the article linked above).

Alex "Oxlade" Chamberlain @DolphHauldhagen

@EliBenPorat @Mind_OverBatter VAA is heavily correlated to both release point (arm angle) and IVB; i have some work on adjusted VAA linked below not to say that adjusting IVB w/r/t arm angle isn't valuable and i'm not dealing with tunneling/synergy here. very similar premises though

blogs.fangraphs.comA Visualized Primer on Vertical Approach Angle (VAA)Let’s add some much-needed context to Vertical Approach Angle.

VAA to IVB R2 = 0.04 (Same parameters as above)

I didn’t see a strong link between VAA and IVB. I double checked that my VAA calculation matched Alex’s. What about VAA +/-? Note, my VAA +/- calc is slightly different than Alex’, but our ordinal rankings are identical. Here are my calcs for comparison (please yell at me if I messed up my calcs).

VAAAA to IVB: R2 = 0.05

I would conclude that the Arm Angle is a much larger explanatory factor for IVB than either VAA or VAAAA.

Relief Pitchers vs Starters

This is, in my opinion, the most fascinating aspect of this all. Angles matter a lot more for relievers than starters. Note that “openers” will be classified as Starters and “bulk pitchers” will be classified as Relievers. I know this is “wrong” and may fix it as some point.

Let’s begin with VAA +/- :

We get an R2 of 0.09 for RPs and 0 for SPs.

For vanilaa VAA, we get 0.04 for RPs and 0 for SPs.

Now for the money chart:

For RPs, arm angle has an R2 of 0.5, compared to 0.17 for SPs. That’s a crazy strong relationship and suggests that we can quantify “relieverish” traits as those by pitchers who rely on their arm angle rather than spin.

Arm Angle Adjusted Induced Vertical Break

I’m going to do a full writeup, but the 101 is that if you do a correlation between FF IVB and value, you get a weak relationship for 2021/2022. If we adjust IVB for arm angles, we get a much stronger relationship. I’ve only done quick research on this, so not ready to publish, but here’s a teaser chart:

Concluding thoughts:

Arm Angles are my new favourite thing, and I plan on including them in my analyses going forward. I’m also thinking I can probably create movement synergy charts that incorporate “expected” movement based on the arm angle. Not sure yet how to do that, but hopefully I fugure it out.