No Pitch Plots today but I do have a new post about quantifying command using release angles that went live on FanGraphs this morning. Here’s the basic idea:
Release trajectories… reliably provide information about pitcher intent like no other variable in the public sphere. In theory, pitchers who have better command should have trajectories — vertical and horizontal release angle pairs — that cluster tightly in specific locations. My statistic — the Kirby Index, named for Mariners starting pitcher George Kirby — will be the first public metric that tests this theory.
I got pretty excited about this about a month ago when I realized release angles were this powerful variable that explained a lot about pitch locations and nobody besides Alex Chamberlain was really talking about them. So I created the Kirby Index, which does a (very basic) job of assessing how good a pitcher is at throwing his four-seam fastball to the exact same location. It turns out that the simple Kirby Index is “stickier” year-to-year than two models (Location+ and PitchingBot) that also attempt to quantify command.
The 2024 Kirby Index to date is linked in a Google Sheet here — I’ll plan to update that Google Sheet every week or so with updated rankings. (For more frequent updates, you can create your own Kirby Index at home using my code.)
I think I started reading Dave Cameron at U.S.S. Mariner when I was in middle school; when he started writing for FanGraphs, I read him there as well. By the time Jeff Sullivan left Lookout Landing for FanGraphs in 2012, I was reading the site frequently, and have continued to do so. Seeing my byline on the same site that published my two favorite baseball writers growing up is pretty fun. I hope you read and enjoy the piece — I’ll be posting a new Pitch Plots about Shota Imanaga on Monday.
Awesome read on fangraphs man. Would you have anywhere to point me to to read or watch more on pitcher trajectory? Any chance you might write something breaking down what the details look like live vs in the kirby index?