The problem with getting deep into individual football statistics (which is what PFF is all about), is that football is the ultimate team-oriented game, which in turn makes individual statistics less meaningful and relevant than they are in other sports. For example it is not like baseball, which is for the most part one-on-one competition, pitcher versus batter. With the evolution of the internet and computers, more and more statistics are readily available compared to past generation, and current sport fans crave those stats - as do the talking heads and written media types for their professions. After all the new stats that became available and used in baseball that were not around thirty years ago, sports fans wanted the same thing for football.
Blend in the fact that the NFL has by far become the nation's most popular sport, and you had the perfect storm for a stat-driven site such as PFF to not only become popular, to be given a free pass by far too many to question the validity of their data. PFF not only took advantage of this opportunity, but also marketed themselves very well.
One way they did this when they were new was to market mainstream sports writers and give them free subscriptions to the content others had to pay for. Writers were sold on the idea that they had exclusive information, giving them a leg up on their competition, which would in turn boost readership, ratings and ad revenue. This in turn gave PFF the exposure that they wanted to a mass audience, and also created demand from those consumers that wanted access to that same content, and would be willing to pay for it.
I have no problem at all for using the site for snap counts and similar information, but to be fair, there are other sites that do offer that same information. The reality is that the people that compile the stats are not professional scouts or coaches, and they don't know what the play call or assignments were. On top of that, they don't even use the available all-22 video to make their determinations; their priority is to get those latest stats out quickly, rather than waiting to make their assessments after the all-22 game tape is available.
Exhibit A: A quarterback throws an incomplete pass, missing his receiver by 6-7 yards. Immediately PFF diagnoses the blame as being solely on the QB, without ever considering any other possibility (e.g., the receiver ran a bad route and was in the incorrect spot).
Whether that is due to lack of training (never having worked as a coach or scout at any level), laziness, marketing (a desire to avoid pointing out a potential error in their stats, which would discredit their 'research'), the bottom line is that the data is corrupt - and therefore if not worthless, at minimum very suspect.
Exhibit B: Many of their stats rely far too much on information that they can not possibly know from watching a televised game, and others are simply too subjective. For example: quarterbacks are rated on throwing under pressure, but conversely quarterbacks who sense the pressure sooner and react accordingly do not get that credit. A quarterback who maneuvers in the pocket to find a passing lane gets no credit in this instance, but a quarterback who has a pass tipped at the line gets that incomplete pass removed from his accuracy percentage. A quarterback who makes the mistake of throwing into double coverage is not chastised, but gets extra points if that pass is completed. Factors such as these make their passer ratings while under pressure questionable at the minimum, if not useless.
Exhibit C: A few years ago PFF's stats came to the conclusion that David Garrard was a better quarterback than Tom Brady; Gary Guyton was a better LB than Jerod Mayo; Stylez G. White was a better DE than Mario Williams and Jared Allen; Lamarr Woodley was better than DeMarcus Ware; Mike Vrabel (with KC) and Tamba Hali were better than Elvis Dumervil; Sione Pouha was a better DT than Vince Wilfork; and Jonathan Stewart, Justin Forsett, Jason Snelling, Ladell Betts, and Brian Leonard were all better running backs than Adrian Peterson.
Those type of rankings should have sent the developers of the site back to the drawing board, but instead they steadfastly defended them as being impeccable and beyond reproach. That stubbornness on PFF's part to defend their analysis rather than to even consider the possibility of the methodology being flawed makes me seriously doubt the validity of any of their research.