by Carl Yedor

Over the next few weeks, we're going to be posting a number of statistics from last year that will be discussed in the upcoming Football Outsiders Almanac 2014. We'll start today by taking a look at running games. Specifically, we will examine how the offense’s success, measured by DVOA, is affected by the number of running backs on the field and how often the offenses used different numbers of running backs. Next week, we will look at it from the defensive side.

NFL offenses are continuing to shift away from the traditional multiple back sets of old, using a single back formation on running plays 60 percent of the time in 2013, up from 56 percent in 2012 and 53 percent in 2011. The arrival of Chip Kelly and his offense in Philadelphia had at least a little to do with that four percent increase.

The Eagles, already a single back-heavy team in 2012 (used on 76 percent of their running plays), went even further in 2013 by using a single-back formation on 98 percent of their running plays. And in their very small sample of multiple back running plays, the Eagles averaged 1.7 yards per attempt and had a DVOA of -66.6%. One might call that devilishly bad, if you didn't realize we were talking about just six plays all year. All the single-back sets definitely paid off, as the Eagles led the league on single-back runs with a 15.1% DVOA, more than five percentage points better than the next closest team.

Going the other direction, the team that ran out of multiple-back formations the most was the San Francisco 49ers, maintaining their hold on the top spot from the 2012 season. The 49ers used a multiple-back formation on 78 percent of their running plays, up from 74 percent of the time in 2012. However, their success on these plays went the opposite direction, falling from a DVOA of 0.4% to -9.9%. Frankly, that seems a little odd given the threat Colin Kaepernick poses to defenses at the quarterback position.

Seattle had the largest gap between their single-back DVOA and their multiple-back DVOA, with a difference of 24.8%. Marshawn Lynch and Russell Wilson certainly made a formidable duo in posting a 9.7% DVOA on single-back runs, and this was even more impressive given the offensive line issues the Super Bowl champs had to deal with during the season.

The Seahawks were closely followed by their foes from Super Bowl XL, the Pittsburgh Steelers, who had a difference of 23.2% between the different types of formations. However, the Steelers’ differential resulted more from their general ineptitude running the ball with multiple running backs (-36.2%) than from being productive with one running back.

On the other end of the spectrum, the Washington Redskins had the largest DVOA difference in the other direction. Robert Griffin and company posted a differential of -23.9%, meaning they were much better with multiple running backs on the field than they were with just one. The Redskins posted a DVOA of 12.2% from multiple-back formations and used two or more running backs on 50 percent of their runs.

The best team at running from multiple-back formations might come as a bit of a surprise, given that they only used those formations 35 percent of the time and were not known as a bruising squad. Green Bay had a 20.5% DVOA from multiple-back formations, which was especially important after Aaron Rodgers went down in the middle of the season.

Below are all the running statistics we keep track of for single- and multi-back formations, sorted by the difference in DVOA between single-back formations and multi-back formations. Denver, Detroit, and Philadelphia all used multiple running backs less than five percent of the time, so we listed their splits separately because the very small sample leads to some occasionally strange numbers. The data uses formation and not personnel, so if a receiver lines up in the backfield, for this study, he gets counted as a back. A tight end lined up at fullback will be treated the same way. No Wildcat-style runs were counted, so plays involving direct snaps to running backs or receivers were left out of the study.