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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, I had questions that traditional box scores were unable to sufficiently answer. I began collecting possession data 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 numerous other companion statistics found on this site were created and refined over the years as a result of those inquiries.

Detailing my approach to possession efficiency in these notes is intended especially to prompt new questions and inspire more contributions to the college football analytics community.

Contact me via email at bcfremeau at 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 four-team 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. I prefer to maintain a closed FBS vs. FBS data set.

 

Possession Types and Results


College football games are contested between two teams as a series of alternating possessions. Since 2007, FBS games have averaged 26.6 total game possessions, 13.3 total posessions per team per game.

Offensive drives (97.1 percent of all game possessions) consist of one or more plays from scrimmage and conclude in one of the following ways:

  • Touchdown (25.2 percent of all offensive drives)
  • Field Goal Attempt (12.1 percent)
  • Punt (38.7 percent)
  • Interception (7.3 percent)
  • Fumble Recovered by the Defense (4.9 percent)
  • Turnover on Downs (5.3 percent)
  • Safety (0.2 percent)
  • End of Half (6.1 percent)

Defensive possessions (1.1 percent of all game possessions) are initiated as a result of an opponent interception or fumble and conclude on the same play with the defense in control of the ball in one of the following ways:

  • Touchdown (96.3 percent of all defensive possessions)
  • Fumble Recovered by the Offense (3.5 percent)
  • Safety (0.2 percent)

Special teams possessions (1.7 percent of all game possessions) are kickoff return or punt return events that conclude in one of the following ways:

  • Touchdown (38.0 percent of all special teams possessions)
  • Fumble Recovered by the Kickoff or Punt Team (52.2 percent)
  • Onside Kick Recovered by the Kickoff Team (9.4 percent)
  • Safety (0.4 percent)

 

Garbage and Non-Garbage Possessions


Unless otherwise noted, all ratings and supporting data found on this site are calculated only after first filtering out garbage possessions, defined as of July 2018, as follows:

  • An offensive possession of two plays or fewer that runs out the clock to conclude the first half and does not result in a turnover, score, or field goal attempt
  • An offensive possession of two plays or fewer 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 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

Since 2007, 10.5 percent of all possessions have been classified as garbage possessions according to these criteria. FBS games have averaged 23.8 non-garbage possessions per game (11.9 non-garbage possessions and 11.2 non-garbage offensive drives per team per game) in that span.