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Monday, November 14, 2011
QBR ranks: Alex Smith and Ginn's drop

By Mike Sando

Alex Smith carried more of the offense than usual in the win against the Giants.
Alex Smith's lone interception Sunday dropped his NFL passer rating for the game from 103.5 to 85.7.

This was unfortunate for the San Francisco 49ers' quarterback because there was nothing wrong with the pass he threw. Receiver Ted Ginn Jr. was open by seven yards on the play, but the pass bounced off his hands. Corey Webster, the New York Giants cornerback in coverage, turned what should have been an 8-yard reception into a pick.

With a reception instead of an interception, and with all else being equal, Smith would have completed 20 of 30 passes for about 250 yards with one touchdown and no interceptions. Instead, he was 19 of 30 for 242 yards with one touchdown and one pick.

None of this affected the game's outcome. The 49ers won, 27-20, and improved their record to 8-1. But statistics do matter. They shape perceptions, frame debates, affect contract negotiations and help determine which players command respect across the league.

This one play in particular also provided a good test case for Total QBR, as several suggested to me Sunday night.

"Do they take into account that the INT was not his fault when calculating QBR?" Justin asked via Facebook.

Over a season, yes. On one play, not as much.

Smith finished the game with a 67.7 QBR. The figure could have been 72.0 without Ginn's drop and the subsequent interception. But that's a simplified answer to a complex question.

ESPN game charters do not determine, on a play-by-play basis, that blame for a certain error fell 100 percent on one player. The QBR formula assigns blame to the degree statistical analysis has determined appropriate over time, not on a specific play. Even on some obvious dropped passes, it's possible the receiver wasn't fully to blame.

I posted Justin's question to Alok Pattani of ESPN's analytics team. How, in the end, did that Ginn drop and ensuing interception affect the QBR score for Smith? His reply:
"The Smith question is difficult and inexact. If Ginn catches the pass, then they are still driving, so there are more plays there for Smith, etc. Then the clutch weight could change for later plays based on the score being different, etc.

"For a simple scenario, let’s suppose Ginn caught it at the 20 and got no YAC (setting up 3rd-and-6 from the 20), then someone else fumbled on the next rushing play and the rest of the game went exactly as it did. Smith would get about 50 percent credit for this play, which would still be negative, but less so. His QBR for the game would end up at 72.0."

Our basic answer, then, was that Smith lost about six percent of his QBR total from this play, assuming Ginn was, indeed, fully at fault for the error. Smith's NFL passer rating fell by about 17 percentage points. Neither measure told us exactly what happened, but QBR came a lot closer. Those interested in a more detailed explanation for dropped passes can check out what Dean Oliver wrote in August:
"Statistical analysis showed that what we call a dropped pass was not all a receiver's fault, either. A receiver might drop a ball because he wanted to run before catching it, because the defense distracted him, because it was a little bit behind him or because he was about to get hit by a defender.

"If the defender was there a half second before, the defender would have knocked the ball free and it would have been called a 'defended pass,' not a 'dropped pass.' There are shades of gray even on a dropped pass, and analysis showed that. Drops are less a QB's fault than defended passes or underthrows, but the QB does share some blame."

Back to Week 10. Smith's showing ranked ninth-best in the league, according to QBR, and Seattle's Tarvaris Jackson was close behind.

Total QBR has heaped praise upon Aaron Rodgers, Drew Brees, Tom Brady, Tony Romo, Matt Hasselbeck, Ben Roethlisberger, Manning and Matt Schaub this season.

Those eight emerged from Week 10 with season-long scores higher than 65, which generally reflects Pro Bowl-caliber play. The first four listed have achieved scores near or above 75, reflecting MVP-caliber play.

The chart shows QBR scores for NFC West quarterbacks by week and for the season.

Quick thoughts on how NFC West passers graded out in Week 10 according to Total QBR, with NFL passer ratings in parenthesis as a reference point:
The chart below shows how quarterbacks from games involving NFC West teams fared in Total QBR for Week 10.