Opportunity-adjusted fantasy points (OFP) strip away player talent and efficiency and focus solely on opportunity.
FORP -- fantasy points over replacement player -- is the difference between a position's actual fantasy point total (FF Pts) and its OFP (expected total).
The "defense" OFP charts below use the same exact formula as the offense, except it's flipped around to show the volume faced by each defense. The defensive charts are different from offense in that they are sorted by FORP, which shows the best (values above zero) and worst (values below zero) defenses against each position relative to the volume faced.
For the complete explanation of OFP and how you can use it to make better fantasy decisions, check out this introduction article.