Introducing the Kirby Index: A New Way to Quantify Command

The FanGraphs Newsletter, May 3, 2024 [READ IN BROWSER]( May 3, 2024 The release trajectory, it turns out, explains nearly everything about the ultimate location of a pitch. Even without incorporating any information about what happens after the ball is released — the spin, the speed, the movement, the air — release angles, alongside release height and width, can tell us with almost perfect certainty where a pitch within a given pitch type will end up. With this finding, we can do a better job of quantifying command. Location+ and PitchingBot Command — two command models hosted here at FanGraphs — reveal a lot about how good pitchers are at avoiding walks, but they take a large sample to become reliable. Both models rely on count-based location outcomes, and it takes a few hundred pitches to gather enough data to meaningfully evaluate locations in each count. They also aren’t particularly “sticky” from year to year, meaning that a pitcher’s 2023 Location+ doesn’t reveal much about what it might be in 2024. What these models capture, it seems, might be fleeting. Release trajectories, by comparison, 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. Michael Rosen's statistic — the Kirby Index, named for Mariners starting pitcher George Kirby — will be the first public metric that tests this theory. For simplicity’s sake, the Kirby Index measures command of a single pitch: the four-seam fastball. But fastballs also present additional complications: Four-seamers can be up, down, in, away, and anything in between. The Kirby Index does not attempt to account for these complexities, but even with significant limitations, it is still “stickier” year-to-year than the two FanGraphs command models. We hope the Kirby Index will be just the first of many efforts to harness the immense power of release trajectories to better understand the elusive concept of pitcher command. [LEARN MORE]( [Bryce Harper Is Getting Comfortable With First Base]( The Phillies star has sound fundamentals at his new position despite his lack of experience. | by Esteban Rivera [The Orioles Are Running Out of Lineup Spots]( Baltimore has a young offense that’s approaching historically significant levels of awesomeness, and more talent is on the way. | by Dan Szymborski [Five Things I Liked (Or Didn't Like) This Week, May 3]( From the thrill of victory to the agony of getting defeated over and over again, this week was full of exciting and delightful plays. | by Ben Clemens [Release Angles and the Illusion of Waste]( Release angles can suggest which pitches look like waste to a hitter — and which ones end up not. | by Alex Chamberlain [Top of the Order: The Twins Are Surging]( The summer sausage has beefed up Minnesota’s offense. Plus, my new favorite one-tool speedster and some Orioles-Yankees thoughts. | by Jon Becker [Where Have All the Home Runs Gone? It's Too Early to Tell]( The league-wide home run rate has fallen relative to last year, but that doesn't mean there's any mischief afoot. | by Jay Jaffe 🎧 [Effectively Wild Episode 2159: The Bees and the Birds]( [DOWNLOAD THE FANGRAPHS APP]( [FanGraphs & Effectively Wild Merch Is Now Available at BreakingT!]( [ORDER HERE]( [Inside Phillies star Bryce Harper's bond with Philadelphia]( by Jesse Rogers, ESPN [A 40-90 season?! This budding superstar is setting a historic pace]( by Thomas Harrigan, MLB [Charlie Condon’s incredible journey from unwanted recruit to college baseball’s premier slugger]( by Seth Emerson, The Athletic ($) [@fangraphs]( [FanGraphs]( [FanGraphs]( [RSS]( [FORWARD]( [SUBSCRIBE]( Copyright © 2024 FanGraphs Inc, All rights reserved. You are receiving this email because you subscribed to the FanGraphs Newsletter. Our mailing address is: FanGraphs Inc 3017 N Underwood StArlington, VA 22213 [Add us to your address book]( Want to change how you receive these emails? You can [update your preferences]( or [unsubscribe from this list](