by Rivers McCown

Continuing our look at game-charting statistics from the 2011 season that'll be featured in Football Outsiders Almanac 2012, this time we'll examine the tendencies and performances of running offenses based on the number of running backs they used. We'll hit defense in Part 2.

One of the biggest changes that happened last season occurred in Indianapolis. And for once, we aren't talking about losing Peyton Manning! No, as Mike Tanier documented in an earlier Walkthrough, the Colts (*gasp*) managed to actually break out the I-Formation from time-to-time as their season spiraled into the abyss. After using formations with multiple running backs on just five percent of snaps in 2010, they were all the way up to 25 percent in 2011. Despite that, the league continued to move more towards single-back sets, and for the first time since we started accumulating charting data, more teams ran out of single-back formations (53 percent) than with two or more backs (47 percent).

Of course, just because they used the I-Formation doesn't actually mean they performed better. In fact, the Colts offense was 25 percent less effective according to DVOA when using two or more backs. That was the fourth largest drop in effectiveness, and two of the teams ahead of them used two or more backs less than 10 percent of the time.

Speaking of ... the new kings of the single-back offense are the Detroit Lions. After two years of mixing in the two-back set at a 25 percent rate, a combination of a breakout Matthew Stafford season and a dearth of talent at running back sent the Lions spiraling down to using multiple running backs in just six percent of snaps. As noted, Jim Schwartz was basically using passes to Brandon Pettigrew as a de facto running game last year.

It only makes sense that you'd use two backs if you only had two good ones, and naturally, the teams that ran with just a single back the most often were generally much worse when they brought another on the field. The lone exception to that is Buffalo, which actually saw its DVOA improve by 25.3% with multiple backs as opposed to one. Corey McIntyre earned his extension prior to the 2010 season -- the Bills also had a better DVOA in multiple-back sets in 2010.

The most effective team out of the single-back? Would you believe the New Orleans Saints? As we noted last year, it's fairly rare for a team to average six or more yards per carry out of a single-back set. The Saints joined the 2010 Texans, 2009 Titans, and 2008 Giants as the only teams to break that mark since we began charting. Replacing Reggie Bush with Darren Sproles seems to be working out pretty well in the bayou, even if nothing else currently is.

There were a select few teams that actually ran more out of multiple-back sets than they did in 2010, but the one that really stands out is the Baltimore Ravens. After spending big on free agent fullback Vonta Leach, 80 percent of their runs came out of multiple-back sets. That was ten percent higher than any other team, and 15 percent more than they used them last year. Dallas came in second, and fellow Harbaugh brother Jim put the 49ers in third place by boosting their multiple-back run usage 12 percent. On the other hand, without Leach, the Texans' usage of multiple-backs on runs declined 12 percent.

In 2010, eight different teams ran with multiple-back sets 65 percent of the time. In 2011, that number was down to just three. The Jaguars, Cowboys, and Ravens are the only three teams to crack the top six in both years.

Below are all the running statistics we keep for single- and multi-back formations, sorted by DVOA from single-back sets. This is about formation, not personnel: if a receiver is in the backfield, for the purposes of this study, he is counted as a back. Also, no Wildcat-style runs were counted, meaning we did not include (among a few other rare things) direct snaps to running backs or receivers.