Quote:
Originally Posted by Matt Arnold
Stuff has been a mix of pitch values and velocity for a while now. Movement can impact individual pitch values, but does not impact the actual stuff rating. That has not changed.
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Before, stuff was supposed to be the reverse of avoid Ks. I saw is a percent of at-bat outcomes. So maybe there was a pitcher who would strike out 20% batters. If his stuff went up, he would strike out 30%. The extra 10% of outcomes that are now strikes took the place of other outcomes, mostly hits. So stuff determined Ks, which would indirectly impact hits against. What the stuff level was before came from several sources, such as individual pitch ratings and velocity, but part of it seemed to be independent as well.
Now, It looks like there is the PBABIP that determines non-HR hits. HRA determines the other hits (HRs). The Ks rate seems to be calculated from that and individual pitch ratings with velocity. Its either a new way of representing the formula to the user or a new formula.