Seahawks run defense is just fine -- so far
A quick glance at the box score from last Sunday's game shows that Seattle's defense gave up 134 rushing yards to the Carolina Panthers, at a staggering rate of 5.2 yards per carry.
By comparison, the league average in most years is around 4.0 ypc. After one week of the 2013 season it's just 3.6. The Seahawks only managed 2.7 ypc.
Cause for concern? Nah.
You'd think a team that can pick up 5 yards on every running play would be unstoppable, rolling over the opposition with such nonchalant ease that they never even have to convert a third down. And you'd be right. But we all know that the average yards per carry includes a messy mix of long runs, short runs, and medium runs. The output from DeAngelo Williams and Mike Tolbert looked like this:
2 carries for 0 yards
2 carries for 1 yard
4 carries for 2 yards
3 carries for 3 yards
2 carries for 4 yards
2 carries for 5 yards
1 each of 6, 7, 8, 10, 12 & 16 yards
I threw out Cam Newton's scrambles, but don't worry, we'll get back to him. What's left is pretty consistent by NFL standards. But would it be enough, by itself, to produce sustained drives? If only we had some magical device that could make random selections from that list of runs, calculate down and distance, and...
Hey, a computer! To make a long story short, I banged out a little script which did just that. It simulated 20,000 drives, with the Panthers starting from their own 20-yard-line and running the ball on every down. A fourth down at the opponent's 28-yard-line was counted as a field goal, and a fourth down behind that was counted as a punt/missed field goal/zero points.
Overall, the simulation produced 2429 field goals (12%) and 2116 touchdowns (11%). If the Panthers had 12 drives per game, that would result in an average of 13 points, which is a pretty good defensive effort (note that Sunday's low score on both sides of the ball resulted from a fast game, with the Seahawks having 9 possessions and the Panthers just 7. Seven possessions with the simulated numbers produces 8 points).
THE BIG PICTURE
The Panthers, of course, did not run the ball on every play. The point of the above analysis was to show that if they had, with the same rate of success as occurred in the game, then the Seattle defense would not have required a better effort or any adjustment to win the game.
Those adjustments to a pass/run balance are described in game theory as an effort to reach pareto efficiency. The idea is quite simple: If you are getting manhandled by your opponent's run game but they cannot pass the ball, the defense needs to adjust to defend the run more-- bring in bigger defenders, "stack the box", etc. Likewise, if an offense is having success with the pass but cannot run the ball, they should pass more often until the defense adjusts. There is a hypothetical equilibrium where play selection and defensive strategy cause both types of plays to have an equal rate of success.
So to really understand how well (or how badly) Seattle defended the Carolina running backs, we need to look at how well they defended Cam Newton. Newton had 23 pass attempts, 1 sack, and 5 rushes for a total of 157 yards. The numbers compare like this:
Carolina Week 1
Cam Newton pass/run = 5.4 yards
Tolbert/Williams run = 4.6 yards
All plays = 5.0
League-wide average week 1
Passing plays = 6.4 yards
Running plays = 3.6 yards
All plays = 5.3
Seahawks week 1
Passing plays = 8.6 yards
Running plays = 2.7 yards
All plays = 6.1
By NFL standards, the Carolina offense was remarkably close to equilibrium. We can credit Seattle's defense with balancing their scheme to perfection. Or we can give the to credit Carolina's offensive play calling. Either way, the Seattle defense produced an above-average defensive effort and it would have been detrimental to commit more resources to stopping the run at the expense of weakening the pass defense.