(Photo by Toni L. Sandys/The Washington Post)

If you ask me who the best fancy stats blogger is, I am going to say myself, so it is no surprise that Richard Sherman says he is the best corner in the NFL.

But ask DeAngelo Hall, and he will say DeAngelo Hall.

And if you are New York Jets corner Dee Milliner, well, you see where this is going.

“The best corner in the league? Me,” Milliner said in an interview Saturday. “I ain’t gonna say that somebody else is better than me.”

There is only room for one corner at the top (and, spoiler alert, it isn’t Milliner), so who is it?

If we are going by a quarterback’s sheer fear to throw at a receiver being covered, then Sherman, a member of Seattle’s Legion of Boom, wins hands down. According to Pro Football Focus, opposing quarterbacks only threw in Sherman’s direction 57 times last season and had just a 36.2 rating during that time – best among the 32 corners who took 75 percent of their team’s snaps last season.

But a cornerback’s job involves more than limiting targets,  intercepting the ball and forcing fumbles, so to quantify all the little things we need to look at player evaluation a bit differently. And that includes considering more advanced metrics such as Win Probability Added and Expected Points Added.

WPA starts with a Win Probability (WP) model of the game of football. Every situation in a game gives each opponent a particular chance of winning, and a WP model estimates those chances. The model created here at Advanced NFL Stats uses score, time, down, distance, and field position to estimate how likely each team will go on to win the game. For example, at the start of the 2nd quarter, a team down by 7 points with a 2nd down and 5 from their own 25 will win about 36% of the time–in other words a 0.36 WP.

We can measure the values of situations and, by extension, the outcomes of plays by establishing an equivalence in terms of points. To do this we can start by looking back through recent NFL history at the ‘next points scored’ for all plays. For example, if we look at all 1st and 10s from an offense’ own 20-yard line, the team on offense will score next slightly more often than its opponent. If we add up all the ‘next points’ scored for and against the offense’s team, whether on the current drive or subsequent drives, we can estimate the net point advantage an offense can expect for any football situation. For a 1st and 10 at an offense’s own 20, it’s +0.4 net points, and at the opponent’s 20, it’s +4.0 net points. These net point values are called Expected Points (EP), and every down-distance-field position situation has a corresponding EP value.

These metrics offer a new framework for evaluating defensive play.

All we need to do is add up all the WPA (or EPA) for each play in which the WPA (or EPA) was positive. “+WPA” and “+EPA” add up the value of every sack, interception, pass defense, forced fumble or recovery, and every tackle or assist that results in a setback for the offense.

What these stats measure is “playmaking” ability. When I watch the NFL Films shows, the sideline audio is usually filled with coaches urging on their players with an emphatic, “Go out there and make a play!” Simply stated, +WPA (and +EPA) puts a number on playmaking.

Here is how the cornerbacks who played 16 games last season rank in terms of +WPA and +EPA. Those in the upper right, the elite corners of 2013, had better seasons than those in the lower left.