PFF looks at stats through their particular set of lenses. I happen to like their overall approach, but that is only my point of view.
The main reason I paid for to get their premium stats was to bring those stats to this forum to help inform our discussions.
Below is an excerpt from their explanation of their grading system. I hope that you find it useful.
1) Why do we grade?
The goal of our detailed grading process is to gauge how players execute their roles over the course of a game by looking at the performance of each individual on each play. We look beyond the stat sheet at game footage to try to gain an understanding of how well a lineman is blocking on a given play, how much space and help a runner is being given on a play, how effectively a pass rusher brings pressure or how well a defender covers a receiver. . We collect lots of extra statistics such as yards after catch, yards after contact, missed tackles, dropped passes etc., but our real focus is on grading individual performance on each play.
Did an offensive lineman seal his block to spring the runner through a hole? Did a defensive lineman beat his block to force a runner to change the play direction in the backfield? Was the crucial third-down completion due to the quarterback beating the coverage or a breakdown in coverage? .
We examine not just the statistical result of a play, but the context of that statistic. The defensive tackle may have made a tackle on a play, but if it was 3rd-and-5 and he got blown 4 yards off of the ball to make the tackle after a 6-yard gain, that's not a good play. .
This allows us to present a unique set of statistics for individual player performance in each game. We present base statistics alongside more advanced statistics together with a grade for every player. The marks are presented as overall composite grades but are also broken down in a number of key areas:.
Offense • Running • Passing and receiving • Pass protection • Run blocking • Screen blocking
Defense • Run defense • Pass rushing • Pass coverage .
.2) What Do We Grade?
Throughout the course of the season (regular season and playoffs) we grade every single offensive, defensive and special teams snap. We log data such as the point of attack of a running play, the location a pass was thrown and hang time of kicks and punts before moving on to the player-performance analysis. . A typical line of analysis will describe an offensive and defensive player being graded for a one-on-one confrontation. This will include their names and grades as well as a comment describing the play. So for example, a match-up between a right guard and left defensive tackle could result in the following comment: .
"The RG drove the DLT down the line of scrimmage opening a wide hole off his outside hip for the running back (##) to pick up the first down on 3rd & 3." . This type of notation serves a few purposes. First, it captures detail for grading, a concise comment that can be referenced back to individual players for further analysis at a later date. Also, due to each play having a unique ID, it also creates a clear and accessible audit trail for all analysis. . .
3) How Do We Grade?
Each grade given is between +2 and -2, with 0.5 increments and an average of 0. A positive intervention in the game rates a positive grading and vice-versa. Very (very) few performances draw a +/-2 rating. In fact, the distribution of non-zero grades is like this: .
+2.00.01percent+1.50.3percent+1.016percent+0.537percent (unbalanced because of the way WRs and HBs are rated)-0.524percent-1.022percent-1.50.5percent-2.00.01percent.
The grading takes into account many things and effectively brings "intelligence" to raw statistics. . For example, a raw stat might tell you a tackle conceded a sack. However, how long did he protect the QB for before he gave it up?
Additionally, when did he give it up? If it was within the last two minutes on a potentially game-tying drive, it may be rather more important than when his team is running out the clock in a 30-point blowout. .
The average grade, or what we would typically expect of the average player, is therefore defined as zero. In reality, the vast majority of grades on each individual play are zero and what we are grading are the exceptions to this. .
A seal block on the backside of a play, for example, is something that it is reasonable to expect to be completed successfully. Consequently, it receives a zero grade, whereas the differentiation between a good and poor block is a heavy downgrade for a failed seal block to the backside of a running play. . .
4) The "Rules" of Grading
Because of the nature of the roles, each position is graded in a slightly different way and the definitions for each run on for many pages. Although we're not going to publish our 30+ page document on how we do this, not least because that's our IP, below are a few of the key principles in our grading methodology: .
• DON'T GUESS — If you're not 95 percent sure what's gone on then don't grade the player for that play. The grades must stand up to scrutiny and criticism, and it's far better to say you're not sure than be wrong.
It is, however, crucial that this is not seen as an excuse to shy away from making a judgement. What we definitely do not do is raise or lower the grading because we're not sure. Giving a grade of -0.5 rather than -1.5 for a player on an individual play because you're unsure is the wrong grade to give. If the grader is 95 percent sure of the severe fault on the play, the grade is -1.5. If, however, the grader is unsure of his judgment, the correct grade is 0. . • WE ARE NOT SCOUTS — We aren't looking for (or grading) style or technique, merely the result of the play. We aren't looking for promise and potential that can be coached up. We aren't looking for things like "heavy-legged waist benders" on the O-line. We aren't looking for DBs with "stiff hips."
We are looking for the result of that poor technique, not the poor technique itself. If poor technique results in a positive play, that is graded at the same level as good technique yielding a positive play. Did the lineman make the block he attempted, by whatever means?
This is professional football, and our biggest assumption (one that we feel, and have been informed, is a very safe assumption) is that the player at least attempted to complete his assignment on an individual play. This removes a large degree of the doubt surrounding us not having access to playbooks and play calls.
We are grading what happened, and it is safe to assume that in the vast majority of cases the assignments carried out were the assignments called on that play. .
• YOU DO NOT HAVE TO APPORTION BLAME ON EVERY PLAY — On each play there is often a "winner." One unit, be it the offense or the defense, will usually get the better of a play by varying degrees. This, however, does not entail that one or more individuals on the losing unit are to blame.
For example, if an offense is stopped on 3rd-and-3 on a running play for 2 yards, that would constitute a failure for the offensive unit. But each member of the offense may very well have carried out his assignment properly.
Say the defense sets up overloaded against the run. Every defender except one is successfully blocked. A lone, unblocked defender makes a strong tackle to stop the back short of the marker.
In that instance, no one individual is at fault for the play failing. The defense simply had the right play called. Sometimes plays are designed badly, sometimes coaches don't adjust. This site is looking at individual player performance, not that of coaches and not necessarily how individual player performance correlates with team performance.
. • GREAT PLAYERS SCREW UP TOO — Blame is apportioned according to who is at fault on the play, not according to seniority. If a veteran QB clearly overthrows a rookie WR, it is not assumed the rookie got something wrong (as some commentators and journalists assume while watching the game live).
We treat players as a number rather than a name and the reputation attached to that name. We treat Ray Lewis as Baltimore No. 52 and see what grade he comes out with at the end for the individual performances in that game. .
• ZERO (0.0) IS THE AVERAGE GRADE — If a player does something you would normally expect, then this scores a 0. If a linebacker makes an unblocked tackle 5 yards downfield or a tight end makes a wide-open catch for an 8-yard gain, they receive a score of 0 for that play.
Grades are given for plays which are reasonably considered to be better or worse than the average or expected play. So for example, if the linebacker were to then force a fumble on that tackle, that would constitute a positive play and a positive grade. If the tight end were to in fact drop the wide-open pass, that would constitute a negative play and a negative grade.