May 2008

PFX vs. BRK and Pitch Types

It’s been a while since we posted a glossary or Q&A explaining some of the features of Gameday, so here’s a link to the one we did last spring.

Also, here are answers to two commonly asked questions about Gameday:

Q: What are the PFX and BRK values?

A: “Break” is the greatest distance between the trajectory of the pitch at any point between the release point and the front of home plate, and the straight line path from the release point and the front of home plate. “Pitch-f/x” is the distance between the location of the actual pitch thrown over the plate, and the calculated location of a ball thrown by the pitcher in the same way, with no spin. Or, in more common terms, this is the amount of “movement” the pitcher applies to the pitch. A faster, straighter pitch like a fastball will have a higher Pitch-f/x value than a slower, breaking ball like a curveball, which will have a higher Break value.

Q: How do you determine pitch types?

A: We compare specific properties of each pitch — its speed at release and where it crosses the plate, velocity and acceleration in three dimensions, as well as angle and degree of break — to those of previously defined “control” pitches, then evaluates the similarity of each property to that of each control pitch to determine an overall likelihood of the pitch type. The most likely pitch type is then selected.

Additional logic is applied to weight the results towards specific pitch types for each pitcher; for instance, this will limit the likelihood of a pitch being labeled as a split-finger fastball if the pitcher is not known to throw this pitch. However, certain pitch types are not completely restricted, in the event the pitcher later introduces that pitch to his repertoire.

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Thanks for everyone’s feedback, we really do read everything even if we don’t respond that often. We hope everyone enjoys the features we have added and changes we’ve made, many of which were in direct response to comments on this blog. Plus, we have some additional cool new stuff that we hope to release within the next few weeks.

Happy baseball!