[BostonCard]

Does PFF watch each player on each play and make a judgement, or is it based on stat outcomes?  

Yes

https://www.pff.com/grades

The PFF grading system evaluates every player on every play during a football game. We believe that #EveryPlayCounts and that attention to detail provides insights and data that cannot be found anywhere else. The grading system was founded on the principle of grading “production” rather than traits or measurables, but perhaps a better way to describe it is a player’s “contribution to production” on a given play.
Did the quarterback make a great throw, but it was dropped? The quarterback contributed to positive production and will receive a positive grade for that effort, even though the receiver let him down, earning a negative grade along the way.

There is still some subjectivity involved, and sometimes it is not clear whose “fault” a given negative play is, without knowing what was called, but in general the system is better than one based solely on outcomes.

BC

[BostonCard]

Does PFF watch each player on each play and make a judgement, or is it based on stat outcomes?  

Yes

https://www.pff.com/grades

The PFF grading system evaluates every player on every play during a football game. We believe that #EveryPlayCounts and that attention to detail provides insights and data that cannot be found anywhere else. The grading system was founded on the principle of grading “production” rather than traits or measurables, but perhaps a better way to describe it is a player’s “contribution to production” on a given play.
Did the quarterback make a great throw, but it was dropped? The quarterback contributed to positive production and will receive a positive grade for that effort, even though the receiver let him down, earning a negative grade along the way.

There is still some subjectivity involved, and sometimes it is not clear whose “fault” a given negative play is, without knowing what was called, but in general the system is better than one based solely on outcomes.

BC