They calculate PPD by eliminating garbage drives or kneel downs at end of game of half
Then I take away pouts from the offense thst the D scores.
Simple math of drives and total points allowed after adjustments
Then you can estimate where those numbers fall based on the weeks ranking on the BCFTOYS website.
The website will have the game stats updated a couple days after all college games are play.
I haven’t been able to find PPD numbers for specific individual games so I have to estimate.