FO has them at 22nd, about 4% below average
FOOTBALL OUTSIDERS: Innovative Statistics, Intelligent Analysis | 2013 DEFENSIVE EFFICIENCY RATINGS
Be skeptical of anything that has them ranked bottom five, as that stat probably isn't adjusting for opponent.
Points allowed includes the worst special teams in the league in there when it's counts how many points this team allowed. That's what I'm saying: if you lump in the special teams with anything, this year's Redskins team becomes historically bad.