Washington Redskins Coach Mike Shanahan said a poor effort by his defensive front was the primary reason for his team’s inability to stop the Minnesota Vikings in Saturday’s loss.

After Viking quarterback Christian Ponder and runnning back Adrian Peterson were knocked out of the game on the first possession of the third quarter, Washington fell against backup quarterback Joe Webb and backup running back Toby Gerhart, who led Minnesota to victory and a 241-yard rushing day.

Barry Cofield (96) is blocked by Minnesota Vikings center John Sullivan (65) as he reaches for Vikings quarterback Christian Ponder (7) Sunday. (Photo by Jonathan Newton/The Washington Post)

Shanahan agreed with Cofield’s assessment.

“Yeah, it wasn’t our best effort on defense this year,” Shanahan said. “Usually, it starts up front and that was probably the poorest game that we’ve played up front this year. Normally, if you don’t have a great outing up front, you don’t have a great game on defense.”

The 241 rushing yards were the most allowed this season by the Redskins, who struggled against the run earlier in the year, but seemed to have shored up that area in the last seven games.

Said Cofield, “We’ve got a lot to think about next week … Hopefully guys use it as a driving force.”

Cofield and the Redskins close out the season Sunday against the Philadelphia Eagles, to whom they surrendered 192 rushing yards in Week 6.