Say what you want about Pro Football Focus, you can't deny they have successful engrained themselves and their analytic tentacles deeply into the football world. Even if their majority shareholder—Chris Collinsworth—wasn't one of the most successful television color commenters on the business, you wouldn't be able to shake a stick at a major football media outlet without whacking into a PFF grade or signature stat.
Given their prevalence, most fans have come across a PFF grade or opinion that rubbed them the wrong way. For your average fan base, this usually occurs when a favorite player gets a surprisingly low grade.