They have won with him playing very well (Sunday against Cleveland, and against Seattle in the opener). They have won with Smith playing below average (at Cincinnati and at Philadelphia, save for a tremendous third quarter against the Eagles).
They have won with him playing poorly (at Detroit, save for the final minutes).
That's a lot of winning for a quarterback with a 19-31 starting record before this season.
Smith is the only quarterback in the NFC West to post a single-game Total QBR score of 70 or higher (50 being average, 100 being maximum). Smith has done it three times, as the first chart below shows. The 49ers have supported him well enough to win three of the four games when Smith's QBR ranged from 10.3 to 47.5.
2011 NFC West: Total QBR
Quick thoughts on how NFC West passers graded out as they did by Total QBR in Week 8, with NFL passer ratings in parenthesis as a reference point:
Alex Smith, 49ers (87.2 QBR, 98.8 NFL rating): Smith completed 15 of 24 passes for 177 yards with one touchdown, no interceptions, one sack and one fumble, which the 49ers recovered. Shouldn't Smith get bonus points for completing passes to left tackle Joey Staley (17 yards) and nose tackle Isaac Sopoaga (18 yards)? As it was, Smith ranked third behind only Matthew Stafford and Michael Vick for highest QBR scores in Week 8. QBR measures by rate. Smith participated in only 31 action plays, fewest among every listed quarterback but Charlie Whitehurst.
Tarvaris Jackson, Seahawks (45.3 QBR, 69.1 NFL rating): Jackson completed 21 of 40 passes for 323 yards with no touchdowns, one interception and two sacks. The Seahawks listed Jackson as the starter, then went with Whitehurst to open the game. Jackson took over quickly once coach Pete Carroll realized the offense was stagnating. Jackson represented a dramatic upgrade from Whitehurst, but was he all that effective? Not by QBR standards. Carroll took heat for botching the final seconds of the first half, but Jackson contributed to the situation as well. He took a 10-yard sack of first-and-10 from the Cincinnati 11-yard line with less than a minute in the half.
A.J. Feeley, Rams (23.3 QBR, 75.8 NFL rating): Feeley completed 20 of 37 passes for 175 yards with one touchdown, no interceptions, four sacks and one lost fumble. Feeley was under heavy pressure from the beginning and had trouble functioning. He held the ball too long in the red zone late in the first half, taking a sack (the Rams scored a touchdown on the drive, anyway). Feeley took a sack and fumbled deep in Rams territory, with the Saints recovering in the end zone. Brandon Lloyd and Billy Bajema dropped passes, but Feeley also missed open receivers, including Lloyd. But his scoring strike to Lloyd was delivered with authority between defenders.
Kevin Kolb, Cardinals (13.0 QBR, 68.2 NFL rating): Kolb completed 10 of 21 passes for 153 yards with one touchdown, one interception, six sacks and one fumble, which the Cardinals recovered. The Cardinals scored two touchdowns on offense, both after taking over deep in Ravens territory (once at the 2, another time at the 25). They managed only a field goal after Kolb's 66-yard completion to Larry Fitzgerald. Kolb ranks last in the NFL, by far, in expected points lost to sacks. Kolb scored minus-6.5 points in that category Sunday, the fourth-worst performance in that category for a quarterback this season (Kolb was minus-6.9 at Seattle in Week 3). Kolb emerged from the Baltimore game with a turf-toe injury.
Charlie Whitehurst, Seahawks (12.8 QBR, 80.7 NFL rating): Whitehurst completed 4 of 7 passes for 52 yards with no touchdowns, no interceptions, two sacks and no fumbles. The Seahawks have essentially given up on Whitehurst. They gave him a chance against Cincinnati to bounce back from a rough outing at Cleveland. When the results were not there immediately, Carroll went with Jackson. Whitehurst might be best suited coming off the bench, when there isn't pressure. He's had only four regular-season starts and needed to make more of this one.
The chart shows how quarterbacks from games involving NFC West teams fared in Total QBR for Week 8. Fifty represents an average performance.