The Clark-Guy example is a reminder of one way PFF grades need to be taken in context.
Clark's defensive snap count (using Football Outsiders) for the first 4 weeks have been, in order, 77%, 75%, 92% and 81% for a season number of 81% on 229 snaps. His snaps increased with the Wilkerson injury. In any case, these snap counts indicate a 3-down player.
Guy's defensive snap count for the first 4 weeks is 51% on 180 snaps. He's not a 3-down player, indicating a specialized role. What would his grade be like if he were forced to play more to his weaknesses?
A PFF grade represents a performance assessment of snaps taken, but there may be a missing element of versatility or "completeness" as a football player in some cases when looking at a grade alone.
To take another example, I could see this utility factor coming into play with edge rushers who are pass rush specialists, rotating in on passing downs, who earn a high pressure-to-snap percentage. How would such players grade in pass rush if they were called upon to play run downs (where teams often pass and often get the ball out quickly) and tweener downs where they would need to react to run or pass instead of just teeing off in the pass rush? That pass rush grade would sink one would think. And if they were plugged in as 3-down player how would they grade against more frequent instances defending the run? Again, not as well.
The problem is not a PFF grading problem. They say what they do--grade every player on every snap. They can't grade a guy standing on the sidelines.
