Often in this space we'll explore the work of someone who had an exceptionally poor performance QBR-wise, or look at why an opponent adjustment may be helping or hurting a QB's numbers. So why are we looking this week at Detroit Lions QB Matthew Stafford, who had an above-average opponent-adjusted QBR of 66.1 in Sunday's win over the Eagles? The reason is that Stafford also happened to possess the highest NFL passer rating of the week at 135.0. Let's take a look at what differentiates Total QBR from Stafford's traditional passer rating:
Don't forget about the fumble
Stafford's passing numbers (19 of 25, 180 yards, 3 TD) last week were fairly impressive. He completed 76 percent of his attempts and threw for three scores without an interception -- all good things. But one area the NFL passer rating fails to account for is when a QB fumbles, yet fumbles are often a big part of the picture of a quarterback's day.
Stafford was responsible for only one turnover, a fumble lost, but it was a potentially costly one. With the Lions up by four and operating at their own 12-yard-line midway through the third quarter, Stafford lost control of the ball while trying to maneuver within the pocket. Officially, the play is recorded as a sack, and the fumble was recovered by the Eagles at the 16, setting them up with a chance to pull within a point with a field goal or take the lead. To put it in terms of their win probability, Detroit went from a 62 percent chance to win before the play to a 50 percent chance after -- a loss of 12 percentage points.
Stafford's QBR fell from 90.5 to 81.0 on the play though his NFL passer rating was unchanged, underscoring the incomplete nature of the latter metric.
Sacks matter too
In addition to the aforementioned sack-and-fumble, Stafford took three other sacks. The first came on the play just before the lost fumble. That, along with a damaging unsportsmanlike conduct penalty on Anquan Boldin, is what helped set the Lions back to their own 12.
Stafford's other two sacks both came on third downs in the fourth quarter. The first turned a third-and-7 at the Eagles 38 (on the verge of field goal range) into a fourth-and-16 and a punt, dropping his QBR from a 76.5 before the play to a 67.5 afterward. His final sack came on a third-and-goal from the Eagles 5. Not nearly as detrimental as the lost fumble or moving out of field goal range, but it also wasn't a positive and did make the ensuing field goal attempt slightly more difficult for his kicker.
None of these plays were accounted for in his NFL passer rating.
How penalties improved Stafford's numbers
Penalties are one area NFL passer rating overlooks and QBR accounts for, and in this case it was actually beneficial to the latter number for Stafford. He was able to draw a defensive offsides call and a pair of defensive pass interference flags, and while none were huge gains for him, QBR does account for these plays.
In the end, the largest differentiators between Stafford's QBR and his passer rating were the four sacks and the turnover. If we look at just his 25 passing attempts, his raw QBR would have been an 81. But losses incurred from those damaging plays get us to his final number of 66.1, highlighting the magnitude negative plays can have on a game.
A look at Stafford's week-to-week progression in the QBR realm: