Win Rating

So this blog is my own weird musings on putting together some kind of football ranking system.  I suppose this all stems from me trying to find something to do while watching football.  It’s not like it’s exactly boring, it’s just I need my mind on something else to stay involved in the game, if that makes sense.  Maybe the best use of my mind, well, I won’t say best use, but a use, is coming up with this ranking system.  In college football, I always considered the BCS computer ranking idea an interesting one.  I mean, think of it, we have arguably the second most popular sport in the country (after the NFL) decided by some system of equations and assumptions.  I like the elegance of the BCS computer over relying purely on polls, it’ll help keep Florida State out of a Fiesta Bowl.  But it seems throughout its history, they’ve been removing variables from ranking system.  For instance, margin of victory is taken out.  Now it’s probably reasonable the BCS has to make changes like that, political pressures and all that.  However, I’m just going do what I feel like here.  I may radically change how I do things at any point, but well, I need somewhere to start from.

In order to come up with any kind of team ranking, the first step is to come up with some way of quantifying a team’s success in a game, think of it as the quarterback rating for the whole team.  This post is purely about putting together that metric.  Here’s the base numbers I’m working with: total offensive yards, points scored, and turnovers.  Points is obvious, and yardage (on both sides of the ball) I feel is a fine indicator of how effectively a team can move the ball, stop an offense, etc.  I’m not considering anything too sexy like pass completion rate, special teams yardage, sacks etc.  For one, it’s hard to get that data in any simple form I can ingest in to a spreadsheet.  And two, I can chug through a lot of seasons by ignoring this information.  So anyway, here’s the three metrics I came up with:

Scoring Efficiency = 100 / (Winner’s Offensive Yards / Total Points))

Yardage Efficiency = (Winner’s Offensive Yards + 38 * Loser’s Turnovers) / (Loser’s Offensive Yards + 38 * Winner’s Turnovers)

Margin of Victory = (Winner’s Points – Loser’s Points) / 7

Now margin of victory is pretty simple, it indicates the number of possessions the winner won by.  For the yardage efficiency, I divide the two yardage values by each other; I feel I can negate any weather / field conditions this way, while still giving a team a way of dominating.  In order to simplify my life, I consider a turnover as a 38 yard play (just quickly, the average net yardage change for a punt in the NFL is 38 yards).  So, if the defense generates two turnovers, I add 76 yards to the total offensive yardage (and if the offense coughs the ball up two times, I add 76 yards to the other teams total offensive yardage).  And then finally, I came up with this metric called scoring efficiency, it finds how many yards it takes to score a touchdown.  It’s my way of approximating stalled drives, failed fourth down conversions, effectiveness of the punting game, and also any special teams touchdowns.  The fewer yards it takes to score a touchdown, the better the team is.

Now to put this all together, I wanted to have a decaying function approaching 1.  I like this idea, I feel it’s a way to take margin of victory into account, where winning by two touchdowns is a bigger deal that winning by three, and is a bigger deal than winning by four, etc.  Also, my goal was to have a bare minimum winning performance to get around 0.5, while any dominating performance will be in the 0.9 range.  So here’s how I combine the values:

Win Rating = exp(-1/(Scoring Efficiency + Yardage Efficiency + Margin of Victory))

For a little example, below are all the games from week 4 of the NFL:

Winner/tie	Loser/tie	Win Rating
St. Louis Rams	Seattle Seahawks	0.808
Jacksonville Jaguars	Indianapolis Colts	0.696
Baltimore Ravens	Pittsburgh Steelers	0.664
San Diego Chargers	Arizona Cardinals	0.896
New Orleans Saints	Carolina Panthers	0.631
Atlanta Falcons	San Francisco 49ers	0.650
Cleveland Browns	Cincinnati Bengals	0.655
Denver Broncos	Tennessee Titans	0.734
New York Giants	Chicago Bears	0.813
Green Bay Packers	Detroit Lions	0.666
New York Jets	Buffalo Bills	0.867
Houston Texans	Oakland Raiders	0.753
Washington Redskins	Philadelphia Eagles	0.669
New England Patriots	Miami Dolphins	0.869

So as you can see, anything in the high .8s is a comfortable victory, while anything in the .6s could have gone either way.  Every week I'll be using this win rating to throw together an overall power ranking - when I put one up I'll tell you how I compute it.