It's no secret by now that Philadelphia Eagles head coach Chip Kelly loves to run the football. The 2013 Eagles finished with an even 500 rushing attempts (4th) for a league-leading 2566 total rushing yards. What's most interesting about Kelly's run-heavy offensive attack is how the success is accomplished.
According to Football Outsiders, the Eagles used a single running back formation on 98% of their runs last season. No other team used a single back formation as often, but the Denver Broncos and Detroit Lions were close at 96% each. What makes this number more impressive is that the Eagles were so successful running out of the single back formation. Philadelphia averaged 5.1 yards per rush attempt (0.9 yards more then the NFL average) and finished with a 15.1% DVOA out of single back sets.
The 2% of the time the Eagles ran out of a multiple back formation only occurred on a total of six plays. In that extremely small sample size, Philadelphia only averaged 1.7 yards per attempt and a -66.6% DVOA.
FO indicates that the single back set is becoming increasingly popular around the league. In 2011, the NFL average stood at 53%. It then increased to 56% in 2012 and then 60% in 2013. Kelly's affinity for running out of 11 personnel (1 RB, 1 TE, 3 WR) is certainly part of the reason for this increase.
It will be interesting to see how these numbers hold up in 2014. The Eagles acquisition of Darren Sproles seems to suggest more multiple-back sets will be used. Even though Sproles catches a lot of passes, both Kelly and Sproles himself have been quick to note he's a running back first and not a receiver.
The Eagles will likely run the ball out of single back sets at a fairly high rate again in 2014 considering their 2013 success. Just don't be surprised to see a decrease to some extent.