DVOA: The main statistic used by Football Outsiders, DVOA (defense-adjusted value over average), breaks down the entire season play by play, comparing the success on each play to the league average based on a number of variables, including down, distance, location on field, current score gap, quarter and opponent quality.
While it can be used as a measure of total team performance, it differs from other power ratings found throughout the Web because it can be broken down to analyze team effectiveness in any number of ways down, quarter, rushing vs. receiving, location on field, passes to backs vs. passes to receivers, etc. It can also be used to analyze specific players.
DYAR: Defense-adjusted Yards Above Replacement. Our metric which takes a player's performance, adjusted for situation and opponent in the manner of DVOA, and then translates it into the approximate number of actual yards that such success (or failure) is worth when compared to a generic bench scrub (also called a "replacement player.") This statistic will increase the rating for players who have a high usage, even if their performance is average, demonstrating the importance of workhorse running backs and receivers who can draw the attention of the defense away from other players.
Adjusted line yards: A stat that attempts to, even to a small extent, separate the ability of a running back from the ability of the offensive line. Adjusted line yards are average rushing yards per play by running backs only, adjusted in the following way
" 0-4 yards 100 percent strength
" 5-10 yards 50 percent strength
" 11+ yards not included
" Runs for a loss 120 percent strength
These numbers are then adjusted further based on game situation as well as quality of opponents faced.
Adjusted sack rate: The total of sacks and intentional grounding penalties, divided by pass plays, which include passes, sacks and aborted snaps. A better measure of pass blocking than total sacks because it takes into account how often an offense passes the ball. It is also adjusted for strength of schedule as well as down and distance.
Drive success rate: The percentage of time that a team will get a first down or touchdown in a given set of four downs. Updated drive stats for 2010 are found here.
Deep passes/short passes: Based on a designation in the official play-by-play, deep passes are those passes that travel 16 or more yards through the air (based on where the line of scrimmage is, not where the quarterback is) and short passes are passes which travel 15 yards or fewer. To the best of our ability, we remove passes that are thrown away to avoid pressure or are tipped at the line.
Situation-neutral pace: Seconds of game clock used per offensive play, with the following restrictions Drives are not included if they begin in the fourth quarter or final five minutes of the first half; and drives are included only when the score is within six points or less. A lower number indicates a faster pace.
Success rate: A measure of running back consistency based on the percentage of carries where the player gains 40 percent of needed yards on first down, 60 percent of needed yards on second down or 100 percent of needed yards on third or fourth down. There is a small adjustment in the fourth quarter based on whether a team is more than a touchdown behind or running out the clock. A running back with a success rate above 50 percent is very consistent; below 40 percent is very inconsistent.
SPECIAL TEAMS STATS
Football Outsiders' special-teams stats translate yards of field position into an estimated value in points using a method that gives each yard line a point value based on the average next score an NFL offense is worth from that point on the field. Punts and kickoffs are based on net yardage. Punt returns and kickoff returns are judged on return yardage only.
Ratings for field goal kickers compare each field goal to the league-average percentage of field goals from that distance.
All Football Outsiders special-teams stats are adjusted based on weather and altitude. They are explained further here.
INDIVIDUAL DEFENSIVE STATS
Plays: Adds together all tackles, assists, passes defensed, fumbles forced or interceptions listed in the standard play-by-play. Does not consider pass coverage where a defender is not listed in the play-by-play.
Stops: The total number of plays by a defensive player that prevent a successful play by the offense, defined as 45 percent of needed yards on first down, 60 percent of needed yards on second down and 100 percent of needed yards on third or fourth down.
Stop rate: Percentage of a defender's plays that are stops.
Defeats: The total number of plays by a defensive player that prevent the offense from gaining first-down yardage on third or fourth down, stop the offense behind the line of scrimmage or result in a turnover.
Football Outsiders game charting project: A group of volunteers who watch tape of NFL games to track a number of statistics not made public by the league, including defensive coverage, formations, pass rushers and blockers, play-action, screens, draws, and quarterback hurries. All data from the game charting project is unofficial, and our numbers may differ from similar data collected by other sources.
Aggressiveness Index: Measures how often a team goes for a first down in various fourth down situations, compared to the league average in those situations, introduced in the book Pro Football Prospectus 2006. The NFL average is represented by 1.0. A coach over 1.0 is more agressive, and a coach under 1.0 is less aggressive.