DVOA: The main statistic used by Football Outsiders, DVOA (Defense-adjusted Value Over Average) breaks down the entire season play-by-play, comparing 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 versus passes to receivers, etc.
DPAR: Defense-adjusted Points Above Replacement. A Football Outsiders stat which compares the performance of each player, in terms of DVOA, to a baseline set not at average but roughly 14 percent below average. 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.
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.
Adjusted Line Yards: Stat which 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-plus 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 2007 are found here.
Deep passes/short passes: Based on a designation in the official play-by-play, deep passes are those passes which 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 thrown away to avoid pressure or 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 only included 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% of needed yards on first down, 60% of needed yards on second down, or 100% of needed yards on third or fourth down. There is a small adjustment in fourth quarter based on whether team is more than a touchdown behind or running out the clock. A running back above 50% is very consistent; below 40% is very inconsistent.
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% of needed yards on first down, 60% of needed yards on second down, and 100% of needed yards on third or fourth down.
Stop Rate: Percentage of a defender's Plays which 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.
Success Rate (defensive backs): Percentage of pass plays where a defender limits the offense to less than 45 percent of need yards on first down, less than 60 percent of needed yards on second down, or less than 100 percent of needed yards on third/fourth down. This is based on which defender is marked in pass coverage by the game charting project and is not based on tackles listed in the play-by-play.
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.