Stands for Pitcher Abuse Points. Only reason I know is because my son is listed.
It's over my head
, but here is the explanation I found.
The basic formula for PAP is a counting stat where, for each appearance, the pitcher is credited with the number of pitches over 100 cubed --
PAP = (NP - 100) ^ 3, where NP is the maximum of the number of pitches or 100. In the essay in the book, they go on to successfully correlate this measure with two different outcomes -- pitchers with higher PAP counts are likely to be less effective later in the season (something which should get every coach's attention), and they are more likely to lose significant time to injury at some point later in their career. The plot of reduced effectiveness with the cubic formation of PAP3 is especially striking.