I saw that. Sometimes they make no sense. I remember JJ Watt (I think) saying how he sat with his coaches and reviewed tape of his performances and then looked at PFF and they were nowhere close.
They have a system, but they also have low paying college kids reviewing tape so sometimes its way off but on average you can get a ballpark sense and over the long run its more accurate. But reviewing tape is better.
I also like to check out Lazar and Kyles all-22 reviews after to see if they kind of agree and normally they are close to what I have, occasionally they point out something I missed, Kyles tends to be a little more lenient than he should be, Lazar is less lenient.
On PFF, for example, Ben Brown had a ZERO pass block grade vs Arizona. They recorded 28 Pass Blocks, 3 pressures and recorded a ZERO grade, never updated or fixed, still there. He had a 29.7 vs Chicago with zero sacks, hits or pressures.
I like to look at PFF and look at discrepancies, but they are prone to making huge mistakes. But they give you some detailed info you can't get anywhere else, just need to know what to use and what not to.
FYI-LB Sione Takitaki was horrible, again, not the best defender LOL