Posted by ESPN.com's Mike Sando
Niners coach Mike Nolan heard about it when he left nickel defenses on the field for the whole game against Seattle in Week 2. The Seahawks rushed 34 times for 169 yards and two touchdowns. On the surface, only a misguided coach would leave five defensive backs on the field while the opponent was averaging 5 yards per carry.
Nolan's plan wasn't misguided at all. This became obvious after breaking down the Seahawks' offensive personnel use in the first half. In theory, Seattle's rushing attack should have enjoyed its greatest advantage while using only two receivers with either two backs or two tight ends. In reality, Seattle ran the ball only five times for 16 yards, a 3.2-yard average, from two-receiver personnel groupings in the first half.
In other words, the 49ers' nickel defense was more successful against the run when Seattle ran variations of its base offense, not when the Seahawks spread the field. The Seahawks gained 76 yards on 10 first-half running plays with three or more wide receivers on the field, highlighted by Julius Jones' 27-yard scoring run.
The plan Nolan implemented had its roots in a 2006 strategy session with former Seahawks quarterback Trent Dilfer, then with the 49ers. San Francisco upset Seattle that season using an early version of the plan Nolan used Sunday. Dilfer knew the Seahawks' offense well enough to know what might disrupt its natural rhythm. The idea was to keep the Seahawks off-balance by using extra defensive backs to facilitate multiple man-zone blitz combinations.
Seattle's depth problems at receiver prevented the Seahawks from countering as effectively as they normally might. A few more personnel-based stats below for anyone interested.
Seattle ran 31 offensive plays against the 49ers in the first half. Thirteen of these featured two receivers. Twelve featured three receivers. One featured four receivers.
Note: By receivers, we mean actual wide receivers, not running backs or tight ends lined up outside. This is a hugely important distinction because defenses match personnel more than they match formations.
Seattle's first-half plays with three wide receivers averaged 7.3 yards per play (the Seahawks needed 8.9 yards for a first down on average).
Seattle's first-half plays with two wide receivers averaged 4.7 yards per play (the Seahawks needed 8.8 yards for a first down on average; all but one of these plays came on first or second down).