Seattle faced its fair share of elite quarterbacks last season: Peyton Manning, Aaron Rodgers, Matt Schaub, Tony Romo, Brett Favre and twice Kurt Warner. It also faced quite a few jobbers: Kyle Boller, Josh Freeman, Matthew Stafford and Marc Bulger. That accounted for some of why Seattle's defense seemed bipolar. Fans understand level of competition, but that understanding doesn't always translate to how they interpret their team's performance. It's a little too abstract.
A big part of Jim Mora's game plan was cap yards and force turnovers. Part of the reason Mora's game plan failed is that Seattle couldn't force interceptions. But to understand how well Seattle forced interceptions, we must understand the expected number of interceptions based on level of competition. It is much harder to win on interceptions against two of the league leaders like Favre and Rodgers than it is against Boller and Stafford.
So, using each quarterback's 2009 interception percentage, I calculated the expected number of interceptions Seattle would have forced if it was league-average at forcing interceptions.
Combined Opponent Interception Percentage: 2.85%
League Average: 16.2
That means Seattle underperformed by about three interceptions or 180 yards. Some of that can be attributed to starting Kelly Jennings, an ailing Marcus Trufant, losing Lofa Tatupu, and, of course, whatever mysteriously happened to Ken Lucas.
A big reason for hope this season is that Seattle faces a schedule of interception-prone quarterbacks and may be able to improve their interception total without actually improving their performance*. Now, there is no perfect way of doing this. Players are injured; players are benched. Performances changes year-to-year. We also can't be sure how many attempts will be distributed between each quarterback. We also can't be sure about the game state, as interception percentage rises when a team is playing from behind and falls when a team is ahead. But the point is to ballpark, for purposes of showing how Seattle can surprise through a "breakout" performance by their secondary.
The average NFL defenses faced 532 pass attempts in 2009. We will use that number for Seattle. The predicted starters for the Seahawks' opponents are Alex Smith, Kyle Orton, Philip Rivers, Sam Bradford, Jay Cutler, Matt Leinart, Jason Campbell, Eli Manning, Drew Brees, Matt Moore, Matt Ryan and Josh Freeman. For each, I will use career interception percentage. Now some players are likely to improve and others are likely to regress, but we can't be entirely sure who will do what, so career percentage will have to do. For Sam Bradford I am using the average of all three first-round rookie starters from 2009: 5.6%.
Away we go!
Combined Opponent Interception Percentage: 3.54%
Expected interceptions: 18.8
Assuming all starters start and perform at their career rate, and assuming Seattle forces only a league average rate of interceptions, the Seahawks can expect to intercept 19 passes this season. That is six more, or an additional 360 yards. That's wins, baby, and one very real reason that should Seattle bounce back in any other capacity, the Seahawks could be a backdoor playoff team.
*And luckily, I would bet good money Seattle will improve its performance.