When the Denver Broncos begin their title defense with Trevor Siemian under center on Sept. 8, they’ll be in a rare spot for reigning Super Bowl winners. Last year’s starting QB, Peyton Manning, retired in March, guaranteeing Denver would become only the fifth champ of the Super Bowl era1 whose opening-day primary quarterback2 during the next season was not the same signal-caller who led the way on Super Sunday.
And even among that group of new QBs, Siemian is almost uniquely inexperienced. Assuming he ends up being Denver’s primary passer in Week 1, he’ll join another Bronco — Brian Griese, who replaced John Elway in 1999 — as the only opening-day primary QBs for a defending champion whose prior career featured both zero career starts and zero points of career Approximate Value (AV).
By contrast, the average defending champ through 2015 returned a QB with 74.8 career starts and a lifetime AV of 66.5, meaning they were both pretty seasoned and pretty good. And that experience has traditionally been an advantage in the pursuit of a repeat Super Bowl bid. All else being equal, teams whose opening-day QBs have more career AV under their belt tend to perform better in the passing game. For instance, a simple regression would predict a 70-AV QB’s team to pass the ball with a half-standard deviation greater efficiency3 — the equivalent of four-fifths of an extra win over a full season — than that of a zero-AV QB, while a more complex fit suggests the same edge in experience could be worth even more, as much as a full standard deviation of passing efficiency or 1.7 wins.
So, given Siemian’s lack of experience (let alone his meager draft pedigree), we’d expect him to lead a passing attack that’s fairly lousy. But even if Siemian spearheads a passing offense with a DVOA index4 of 90, two-thirds of a standard deviation worse than NFL average — as the average zero-AV opening day starter has during the Super Bowl era — it would represent an improvement to the Broncos’ passing attack.
Simply put, Denver won the Super Bowl last season in spite of its passing offense, not because of it. In terms of passing efficiency, the Broncos were an entire standard deviation worse than league average last season, which equated to the NFL’s eighth-most inefficient aerial attack. And Manning himself was awful, producing the worst season of any Super Bowl QB in history. His backup, Brock Osweiler, wasn’t great either, but if Siemian’s 2016 performance can mimic Osweiler’s more than Manning’s, the Broncos will still be better through the air than they were a year ago.