Wednesday, October 12, 2011
Explaining the Rodgers-Tebow QBR caper
By Kevin Seifert
I've been limiting our discussion of Total Quarterback Rating (QBR) to one weekly post, which I caught up on Tuesday afternoon. Since then, however, a number of you have asked how the Week 5 performance of Green Bay Packers quarterback Aaron Rodgers (396 yards) ranked slightly below that of Denver Broncos quarterback Tim Tebow (79 yards).
During his radio show Tuesday on ESPN 540, Rodgers himself said he was "surprised" and "chuckled to myself" upon seeing the rankings on ESPN's television crawl.
"I played a full game," Rodgers said. "He played a half. He completed four passes. I completed 26 …."
I sought an explanation from ESPN's analytics team, which provided a pair of blog posts that explain the apparent discrepancy. Jeff Bennett, ESPN's senior director of production analytics, answered a few follow-up questions as well.
Some bullet points for those interested:
- QBR is a per-play evaluation, so it evaluates what Rodgers did on 47 "action plays." Tebow had 16 "action plays." It's a little bit like comparing a pinch hitter in baseball to someone who played nine innings. QBR is explained as a measure of efficiency at any given moment, not necessarily over the same time period.
- QBR evaluates a wider spectrum of quarterback play than completions and yards, including sacks, scrambles and passing yards after the catch.
- Tebow scrambled six times for 38 yards and a touchdown, giving him considerable credit. Rodgers' only "carry" was a one-yard kneel-down to end the game.
- Rodgers took four sacks. Tebow did not have a play that resulted in negative yardage. Quarterbacks are given a share of blame for sacks.
- Almost half of Rodgers' passing total, 197 of 396, was judged to come after the catch, for which quarterbacks receive less credit.
- QBR weighs a quarterback's performance relative to the game situation. Here's how Bennett described the difference between how QBR viewed Tebow's clutch performance and how it viewed Rodgers': "Rodgers performed about the same as Tebow in bringing his team back from a 14-0 deficit (QBR of 83.6 from start of 2nd qtr). However, unlike Tebow, Rodgers was on the field when he team went into as 14-0 hole. Since those plays count towards his overall [performance], his QBR was 82 for the game."
I'll let that explanation stand on its own merits other than to say Rodgers' QBR of 82 is an elite grade. Here's another way to look at it: Rodgers' passer rating (117.1) was higher than Tebow's (101.7), but passer rating doesn't include many of the components that made Tebow's performance uniquely special. I'm not sure that I like comparing individual QBRs because it weighs game factors that are self-contained and don't always relate.
All this comparison tells me is that Tebow did more to nearly defeat the San Diego Chargers than Rodgers needed to do for the Packers to beat the Atlanta Falcons. It doesn't tell me that Tebow played better than Rodgers. If that makes sense.