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Saturday, August 4, 2012

Point impact estimator

This is a first step in scientifically measuring the impact of a play on a game's outcome. Using every FBS game from the 2011 season, I estimated the point value of a possession by its location on the field. In other words, if a team has the ball on their own 20 yard line, how many more points can they expect, on average, to score over the next several possessions than their opponent?

From that point we can estimate the Point Impact of a play or series of plays by subtracting the point value of a possession (Exp. Point Value) before the play from that point value after the play.

In the app above, you can manipulate these values for yourself. By default, the field position before and after the play is the team's own 40 yard line (and, therefore, the point impact is 0). Change the Yard Line value to any number between 1 and 50. Enter any value in the first column to make that statement true (or clear the box if the statement is false). For example, put a "1" in the change of possession box and you will get a point impact of -5.313. In other words, a team turning the ball over on their own 40 yard line costs them, on average, 5.313 points. Clear the values from the change of possession and 'field position 2/own' boxes and you will see that moving the ball 20 yards across midfield is worth 1.420 points. (Note: this assumes we are always dealing with first down situations with plenty of time remaining on the clock).

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