What is a reasonable goal when starting quarterbacks gets injured? Given the current state of development at the position, I suggest a modest one: Hold on for dear life.
Backup quarterbacks can provide a spark, either through injury relief or via a benching of the starter, but an extended lift beyond previous performance is usually the exception.
The chart documents 12 teams who have undergone significant quarterback upheaval this season, mostly through injury but sometimes because of poor play by the starter. Some teams have won more frequently with their backups, but in total the winning percentage of the starters for those teams (.324) is nearly identical to that of the backups (.326).
In some cases, a swing toward the backups reflects a poor original decision on the starter. The Cleveland Browns are the most obvious case, having won four games with backups Brian Hoyer and Jason Campbell while losing all four of Brandon Weeden's starts.
In other instances, most notably the Philadelphia Eagles, teams have found a groove while the backup was playing. I don't want to take anything away from Nick Foles, who is 4-1 as the Eagles' starter. He has thrown 16 touchdowns without an interception, but it's important to understand how much he has benefitted from LeSean McCoy's NFL-leading 1,009 rushing yards. According to ESPN Stats & Information, nine of Foles' touchdown passes have come among his 46 play-action attempts, an incredible ratio that doubles what we've seen this season from Peyton Manning (eight in 98 attempts), Russell Wilson (eight in 92) and Drew Brees (seven in 92).
Perhaps the best case study for the impact of planning, or lack thereof, at quarterback depth is in the NFC North. It could, in fact, determine the division winner.
The Chicago Bears made an early offseason decision to keep veteran Josh McCown as Jay Cutler's backup, giving him maximum time to train in coach Marc Trestman's offense and to learn the team's personnel as best he could. McCown is 2-0 as a starter this season following a series of injuries to Cutler, keeping the Bears in the middle of the division race. I would regard McCown as an exception, which by definition puts the Bears in an exceptional position as the starter rehabilitates.
The Green Bay Packers, meanwhile, gave up on backup Graham Harrell at the end of the preseason and didn't see enough development from another quarterback, Vince Young, whom they signed hastily midway through training camp. The timing of those decisions left them to sift through discards on the eve of the regular season. Veteran Seneca Wallace, who was out of football last season, became Aaron Rodgers' backup, and Scott Tolzien signed to the practice squad.
Wallace could not rally the Packers in Week 9 after Rodgers fractured his collar bone, and the Packers have now lost three consecutive games. Rodgers is expected to return in the coming weeks, but the team's performance without him leaves almost no wiggle room in the playoff race.
This is but a half-year snapshot in an annual discussion. Given the NFL's current roster and development arrangement, it's almost unfair to criticize a team for slipping without its starter. But this season, at least, it seems likely we will see a few teams reach the playoffs on the strength of their quarterback depth, and perhaps a couple more miss the postseason because of its weakness.