It was kind of a big day for Pro Football Focus, the NFL sabermetrics and tape-grading site that has become a major player in a few short years. With a solid writing staff and 12 film graders who work every game from the preseason to the Super Bowl, PFF has become a fairly indispensable tool for those in the media (and in the league) who want to add another dimension to what they do.

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Thirteen NFL teams have consulted with PFF and purchased their information for use in their processes, and on Monday morning, TheMMQB.com's Peter King reported that former NFL receiver and current Sunday Night Football color man Cris Collinsworth had bought a stake in the company last week. Collinsworth originally got in touch with PFF founder Neil Hornsby a couple of months ago, and realized that the site's grading was, in some cases, more accurate than his own.

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"What really impressed me," Collinsworth told King, "is the fact that 13 NFL teams have contracted with Pro Football Focus for their data. I mean, I have been around the NFL for over 30 years, I know how hard it is to get behind the wall of those teams. And they’ve got 13 teams to trust their data. That’s huge.”

Well, PFF hasn't broken through every wall. On Monday afternoon, new Minnesota head coach Mike Zimmer ended the opening statement of his press conference by giving his piece on PFF and those outside the league who would dare to analyze what happens between the lines.

"The last thing that I want to talk about before I let you guys go is this Pro Football Focus thing," Zimmer said. "I know everybody wants to get the scoop on this, but quite honestly there’s not really anybody... I look at the grades and I can’t tell you what a 0.7 is or anything like that, but I know that the people that are grading our games and our defenses and our offenses, they don’t know if the tackle gets beat inside, if we weren’t sliding out to the nickel or who our guys are supposed to cover. I guarantee they don’t know who is in our blitz package and what they are supposed to do. I would just ask everybody to take that with a grain of salt, including our fans. We as coaches get paid a whole bunch of money to do the jobs that we do, evaluate the players that we evaluate and grade them how we grade them and not based on someone else.

"That’s off my chest, go ahead."

We're not sure exactly what Zimmer was unhappy about -- the Vikings trounced the Chiefs, 30-12 in their Week 3 preseason game -- but PFF did give negative grades to left tackle Matt Kalil (for giving up five pressures, four of those to super-stud Chiefs outside linebacker Tamba Hali) and rookie outside linebacker Anthony Barr.

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Steve Palazzolo, who wrote the game review, wondered why the Vikings put Barr in coverage so often. Palazzolo also pointed out that through three preseason games, the Vikings put Barr (primarily a pass-rusher at UCLA) on the rush 14 times compared to 50 snaps in coverage. Palazzolo didn't specify whether some of those coverage snaps came on zone blitzes or other defensive schemes, and perhaps that's what got Zimmer's goat.

I reached out to Sam Monson of PFF for a response.

"I understand Mike Zimmer’s reservations, but while coaches like to maintain the mystique of football, the bottom line is most plays are simple enough to decipher," Monson told me. "We won’t get everything 100 percent right, the same way the Vikings won’t get everything 100 percent right when watching tape of any other team in the league – it doesn’t mean they’re not right most of the time and it’s still not a worthwhile exercise.

"We would never want anybody taking our grades and stats as the definitive answer to any question. Football is way too complex for that. But they provide a fantastic starting point and can give you a big shortcut to answers you might be looking for. PFF currently sells to 13 teams and once we get to sit down with people within organizations they immediately recognize the value of the grading and what we do -- from coaches to the scouting department to the analytics guys. If Coach Zimmer wants to learn a little more about PFF and our processes, we’re always here."

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​As someone who has written for Football Outsiders for years (the Coke to PFF's Pepsi, and the fundamental originator of NFL sabermetrics on a national public scale) but is well aware of what I don't know, I come down on both sides of this. I'm a huge fan of what PFF does -- they've really sharpened up their writing, analysis and tape work in the last couple of years, and I have no reservation using their metrics in my own work.

However, I've never been very fond of any single-point grading system -- the game is too complex to draw it down to a number, no matter how may decimal points you put behind it. PFF always explains their grades, but I would love to see more words behind those specific numbers. Those numbers don't tell the whole story, and while the PFF guys will be the first ones to agree with this, it's still easy for some to mistake a shortcut for empirical evaluation.

I also agree completely with Monson. If you watch enough tape and learn from enough people in and out of the league who know more than you do, you can discern when a team hits a nickel defense, or blocks inside, or has certain coverage concepts in a general sense. You won't always know what those assignments are, but as many people have said over the years, perfect is the enemy of good.

If you wait until you have enough information and enough connections to get it right every time, you'll never get the bat off your shoulder often enough to get anything right one time. PFF does the best they can with the information they're given, and they do a pretty solid job, as do many other analysts, paid and unpaid, who don't work directly for the league. That may counter Zimmer's seeming insistence that those in the league know best, but that's the way it goes.

Zimmer may find that reaching out to Pro Football Focus, and perhaps even availing himself of their services, could help his own case down the road. One thing's for sure -- more and more teams are using all kinds of information from all kinds of different sources, and the teams who hang back will eventually be a bit behind the curve.