by Sterling Xie

Our current football terminology is going to cause a lot of confusion for future fans if it doesn't change. Just as modern defenses use sub packages roughly three times as often as base personnel, current offenses no longer use "regular" personnel (two running backs, one tight end, two wide receivers) that regularly anymore. As we lead up to the publication of Football Outsiders Almanac 2015, we're continuing to peel back the curtain behind some of the charting stats you'll see in the book. Today, we'll look at offensive rushing success based on number of backs in the backfield.

As you might expect, offenses are increasingly eschewing I-formation football in favor of single-back sets. The league-wide percentage of running plays from sets with two or more backs has declined every single season since 2008, and is now down to 33 percent after sitting at 40 percent in 2013 (for reference, I'm referring to all plays with multiple running backs as "two-back sets" the rest of the article, since we charted a grand total of 15 runs from three-back sets last year). Only one team used it on more than two-thirds of their running plays, and we'll get to this seemingly backwards franchise shortly.

An interesting trend has seen teams hiring playcallers that not only reduce two-back usage, but ignore it completely. Recall from last year's article how the Broncos, Eagles, and Lions were all outliers that used two-back sets on four percent or fewer of their running plays. This year, we have four teams in the disqualifying italicized red font on the table below. Along with Denver and Philly, the Dolphins and Steelers also fell into the red, as none called more than 35 two-back rushing plays all season. The Eagles only ran two such plays all season! Both calls came against Dallas, one in each game, and both went for a single yard. The second one actually resulted in this Darren Sproles touchdown with LeSean McCoy throwing quite possibly his only lead run block all season. Hence, the Eagles are technically your 2014 leader in two-back rushing DVOA.

(Ed. Note: Part of the confusion here comes from how to mark certain formations. We tell charters to mark plays based on where players are after motion. The Eagles run a number of plays which start with two backs, then one back goes in motion towards the outside and the quarterback snaps the ball while the back is on the move. These get marked as "single-back," and for the purpose of comparing running plays, that seems appropriate. -- Aaron Schatz)

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Anyways, with how incestuous the football coaching family is, the next generation of coaches might further disseminate single-back personnel sets. Throwing out the Bengals and Chargers, who promoted from within, seven teams went outside the organization to hire new offensive coordinators before last season: Washington, the Dolphins, Texans, Cowboys, Giants, Lions and Vikings. Five of those teams saw their two-back usage decline by at least 10 percent, and Miami, Minnesota, and Houston were the three biggest usage decliners from 2013. The other two teams, Detroit and Dallas, were at the other end of the extreme, as those two offenses saw the largest and fifth-largest increase in two-back usage, respectively.

Even ignoring the passing game, one-back sets are also becoming more popular because they're just generally easier to run out of, since defenses are likelier to counter with smaller sub packages and fewer men in the box. The league average DVOA figures over the past eight seasons bear this out:

Though two-back DVOA was a smidgen higher in 2009, the two-year rolling averages show a defined separation that has remained fairly constant. You'll notice that one-back sets aren't exactly fending off the decline of the running game as a whole, but the drop-off hasn't been as steep the past two to three seasons.

We'll move towards more team-specific talk shortly, so let's get to the numbers. The table below includes yardage and DVOA stats for single- and multi-back formations. As alluded to above, four teams were small sample size outliers, so we've listed their numbers separately and excluded them from the league-wide DVOA and yardage rankings. 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, although a tight end lined up in a wing position (i.e. right behind the tackle's hip on either side) is not. No Wildcat-style runs were counted, so plays involving direct snaps to running backs or receivers were left out of the study. The table is sorted by two-back rushing play percentage, and in the difference column, a negative DVOA means a team was better in two-back formations than it was out of one-back formations.