NFC West defenses and getting off field

We left off Thursday discussing potential fatigue concerns for the San Francisco 49ers' highly productive, highly experienced defensive line.

The way defensive coordinator Vic Fangio sees things, the 49ers can worry less about their linemen wearing down if the defense plays well enough to avoid too many sustained drives. These sustained drives would force more frequent substitutions.

2011 Defensive Drive Lengths (by plays)

From there, Marty Callinan of ESPN Stats & Information passed along figures showing the 49ers ranking fifth in three-and-out drives forced last season, best in the NFC West.

Marty also passed along information showing how long NFC West defenses were typically on the field during a given drive. The chart breaks down the findings.

San Francisco and Seattle limited opponents to four or fewer plays on more than half of drives. Both also were better than their NFC West rivals in limiting drives lasting between five and nine plays.

The numbers for drives lasting 10-plus plays get interesting. The Rams allowed a lower percentage of these drives, probably because opponents required fewer than 10 plays to score. Seattle allowed a higher percentage of these drives despite having a generally strong defense. An improved pass rush could help bring down those numbers some.