Previously the domain of Maytag and Whirlpool, spin rate has been established as part of baseball’s analytical vernacular over the last few years. Just as it’s statistical brethren like exit velocity and launch angle have changed the way hitters are viewed, spin rate — expressed in terms of RPM — is a way to measure a pitch’s efficacy.
That’s obviously a very imperfect definition and it’s not a simple matter of the highest spin rate generating the best results, but there are some basic truths we can establish. Just as a higher exit velo will generally result in more hits, a higher spin rate will generally yield pitches that are harder to hit.