Peyton Manning completed 5 of 20 passes for 35 passing yards and four interceptions Sunday against the Kansas City Chiefs before he was removed from the game. The Denver Broncos lost 29-13.
And while head coach Gary Kubiak noted afterward he regretted starting Manning because of the nagging injuries the 39-year-old quarterback has been dealing with, Manning's performance could make you completely forget the Broncos are 7-2. After all, this team was built for the Super Bowl, not the playoffs, and this is just the latest in a number of bad games by Manning. It was bad but not completely out of place.
Going into Sunday's game, Manning ranked 21st out of 32 qualified quarterbacks in QBR, and that ranking isn't going up after his performance.
This has been anything but a steady decline for Manning, as last season he finished third in QBR and near the top of the list in a variety of statistics, and that's even while he battled injuries late in the season. It raises some questions. Is this dramatic decline normal? Will he bounce back?
It's common ground in sports analytics to measure a player's improvement and then their decline as they age. This helps teams project performance over a player's career and yields insight during contract negotiations. Quarterbacks tend to peak around age 28 and, on average, appear to steadily decline after that. But that apparent steady decline with age obscures what's really happening. The final year of a quarterbacks's career averages a decline of 0.75 yards per attempt (adjusted for interceptions). In simple terms, this is far worse than any one year of average decline due to age.
In fact, the last year of a quarterback's career falls off by an equivalent of about six years of average age-related decline. If we remove the last season of every QB's career from the data, age-related decline disappears.
The bottom line is successful quarterbacks -- players such as Manning -- don't become worse slowly. All of sudden, one year, their numbers just seem to fall off a cliff, and Manning's numbers fit this profile perfectly.
Established franchise quarterbacks are successful right up until one day when they're not. One day it will happen to Tom Brady and Aaron Rodgers, too. And we won't see it coming. But, of course, everyone will pretend they did.