QBR: No such thing as passer perfection

The official NFL stat sheet said Kurt Warner played a perfect game for the Arizona Cardinals against Miami back in 2008.

Total Quarterback Rating (QBR) knew better.

2008-10 QBs: Chasing Perfection

While Warner was brilliant that day, completing 19 of 24 passes for 361 yards and three touchdowns, his performance could have been statistically superior. He scored a 97.7 on the 100-point QBR scale.

Warner took two sacks for 12 yards in that game, affecting his QBR. The 75-yard touchdown pass he threw to Larry Fitzgerald traveled only 17 yards in the air. About half his passing yardage that day came after the catch.

QBR, set to debut during a "SportsCenter" special Friday night, keeps moving the carrot as quarterbacks chase perfection. Albert Larcada, ESPN Stats & Information analytics specialist for the QBR project, illustrated how this happens by analyzing the three performances since 2008 featuring 158.3 ratings.

Drew Brees posted a 158.3 rating against New England during the 2009 season. That effort translated to 98.6 by QBR standards. Brees took one sack for 4 yards. The 18-yard touchdown pass he threw to Pierre Thomas featured 25 yards after the catch. (Thomas caught it behind the line of scrimmage.)

No matter how well a quarterback plays from a statistical standpoint, he could have fared better.

Completing all 20 pass attempts, each for a 99-yard touchdown, would shatter records. But the performance wouldn't rate as high as one featuring 21 touchdown passes of that length. And so on.

That's why it's misleading to say a quarterback played a "perfect" game when his passer rating maxed out at 158.3 under the formula in place since 1973.

Tom Brady's 158.3 rating against Detroit last season translated to 94.6 in QBR. Brady's receivers made huge gains after the catch in that game, to a degree much greater than they would have done typically.

In theory, a perfectly executed short pass could free up a receiver for additional yards.

"It’s true a perfect pass could set up additional air yards for a receiver," Larcada explained, "but on average we found YAC to be mostly on the receiver, and pretty strongly so. Good receivers get more YAC per completion than bad receivers. Good quarterbacks don’t necessarily get more YAC per completion than bad ones."

More YAC means fewer air yards when all else is equal, hurting a player's QBR number.

"Even with a perfect pass, the receiver still must have the speed/moves/quickness to create the additional yardage," Larcada said.

QBR takes into account many more variables. It grades each play in relation to how it affects game outcomes, putting more weight on a killer interception than a meaningless one on a Hail Mary at the end of a half.

We'll continue the discussion Thursday.