Possession Efficiency Notes

I'm frequently asked questions about the origins of my work with college football data. After witnessing a 2002 victory by Boston College over Notre Dame, a game in which the Eagles failed to advance a single offensive drive across midfield and the Irish had six drives fail inside the BC 25-yard line, I had questions that traditional box scores were unable to sufficiently answer. I began collecting possession data soon thereafter; to define the fluid value of field position, quantify the impact of turnovers and special teams, evaluate offensive and defensive team strengths, and develop new measures of success. The Fremeau Efficiency Index (FEI) and other possession statistics found on this site are the results of those initial inquiries, and many more since.

These notes, detailing my approach to evaluating possession efficiency and providing additional context to the numbers, are intended especially to prompt new questions and inspire more contributions to the college football analytics community.

Contact me via email at bcfremeau@gmail.com and follow me on Twitter @bcfremeau. 

 

Game Results

FBS (Football Bowl Subdivision) college football teams generally schedule 12 regular season opponents, and sometimes play additional post-season games in conference championships, bowl matchups, and in the College Football Playoff to conclude the season. The vast majority of games played are against fellow FBS opponents, but many teams also schedule one (or more) games against FCS (Football Championship Subdivision) opponents. The results of those FBS vs FCS games are not included in the data sets used in my analysis.

Why? FEI team and unit ratings published here are opponent-adjusted, and I'm not comfortable making such adjustments without confidence in the relative strength of each opponent. I have not yet developed FCS team or unit ratings I can trust. Further, FBS vs FCS games are frequently mismatched, and possession results from these games can skew a team's unadjusted possession efficiency data. To fairly evaluate teams, I prefer to maintain a closed FBS vs FBS data set.

 

Possession Types

College football games are contested as a series of alternating possessions between two teams. A possession typically consists of a scrimmage play or series of plays in which the team in control of the ball attempts to advance the ball in order to score while its opponent attempts to deny that effort. I define possession types as follows:

• Offensive Drives (96.8 percent of all possessions) consist of at least one scrimmage play run by an offense in possession against the opposing team defense. Drives conclude in one of eight ways: touchdown, field goal attempt, punt, turnover on downs, fumble, interception, safety, or time expiring at the end of the half.
• Field Goal Attempt Possessions (0.02 percent of all possessions) are situations in which, due to limited time remaining at the end of the half, no offensive scrimmage plays are run and only a field goal is attempted.
• Defensive Possessions (1.1 percent of all possessions) are initiated as a result of an opponent interception or fumble and, with the defense in control of the ball, conclude on the same play in one of three ways: touchdown, fumble recovered by the offense, or safety.
• Special Teams Possessions (1.6 percent of all possessions) are kickoff return, punt return, or failed field goal return events that conclude in one of four ways: touchdown, fumble recovered by the kicking team, onside kick recovered by the kickoff team, or safety.
• Overtime Possessions (0.5 percent of all possessions) include overtime offensive drives (teams alternate drives starting at the opponent's 25-yard line), overtime field goal attempt possessions, overtime defensive possessions, and overtime conversion possessions in which teams alternate two-point conversion scoring attempts from the opponent's 3-yard line.

 

Garbage vs Non-Garbage Possessions

Unless otherwise noted, all ratings and supporting data are calculated only after first filtering out garbage possessions, defined as of February 2021, as follows:

• An offensive possession of two plays or fewer that runs out the clock to conclude the first half, or that runs out the clock to conclude the second half with the score tied, and does not result in a turnover, score, or field goal attempt.
• A possession in the second half of a game in which eight times the number of the losing team's remaining possessions plus one is less than the losing team's scoring deficit at the start of the possession.
• An offensive possession of two plays or fewer by the losing team with a score deficit greater than eight points that runs out the clock to conclude the game.
• An offensive possession or non-offensive scoring possession by the winning team leading by eight points or fewer at the start of the possession that runs out the clock to conclude the game.

From 2007 to 2023, 10.7 percent of all possessions have been classified as garbage possessions according to these criteria. FBS games have averaged 26.2 total game possessions and 23.4 non-garbage possessions per game in that span.