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Friday, February 8, 2013

Yards per Pass+

Aaron Murray was the country's most effective passer in 2012 and it wasn't even close.

One of the initial motivations behind CFBTN was to find new ways to compare teams and players across conferences and across the country. The unique challenge with college football is that there are many teams, few games, clustered schedules, and huge disparities across conferences. For example, how do you compare Johnny Manziel and Jordan Lynch when they don't play any of the same teams or even the same caliber of opponent?

To that end I have developed an algorithm that attempts to answer that question. Essentially, it attaches a value to offenses and offensive players and defenses and uses those values to predict an outcome - e.g., yards per rush. It then compares the predicted values with actual values from actual games and makes adjustments as necessary. The process repeats (dozens or hundreds of times) until the predicted values are as close to the real values as possible. We will never get a perfect fit, but the values generated by the process are the best possible estimates of a team's or player's proficiency in that particular area.

I call these "plus" statistics - e.g., YPP+ (yards per pass plus). Instead of reporting what the team or player actually did during the season, they report what they would have done against a schedule of average opponents. Unfortunately, for quarterbacks I cannot adjust for a player's own team, so a player on a better team (better offensive line, better receivers) playing against this schedule of average opponents has an advantage over another player on a lesser team.

There are many ways of measuring a passer's efficiency, but the one that offers the most bang for the buck is yards per pass, or, even better, yards per pass+. Below is the top 25 by YPP+ and their national ranking in YPP among players with at least 200 pass attempts. For comparison is the top 25 defenses. The dYPP+ means, for example, that Florida allows 2.51 fewer yards per pass than the average defense.

Against an SEC schedule, Aaron Murray averaged 10.1 yards per pass, but should have averaged 10.4 yards per pass against an average schedule, a full yard better than any other quarterback with a significant number of attempts. He faced two of the top four and three of the top 10 defenses by dYPP+. Manziel managed 8.5 YPP despite 4 of the top 10 defenses by dYPP+, but few teams were worse than Louisiana Tech (West Virginia was one of those teams).

More impressive was Taj Boyd, who faced three of the top four defenses by dYPP+ and averaged 9.1 YPP. Nick Florence's 9.3 yards per pass was inflated by his 51 attempts against West Virginia (#118), but brought back down by games against Oklahoma (#7), Kansas State (#13), Oklahoma State (#15), and TCU (#16). McCarron matched Florence with 9.3 YPP and YPP+.

Missouri's James Franklin wins the award for toughest schedule for throwing 51 passes against Florida, a third of his passes against Florida, South Carolina and Vanderbilt (all in the top 20) and half against those three and Georgia (who came in at 33rd). He missed games against Arizona State (#9), Alabama (#10), and Texas A&M (#27); Berkstresser didn't attempt enough passes to qualify for this list, but  otherwise could have claimed an even tougher schedule than his Missouri teammate.

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