Harvard Sports Analysis Collective

In the 2008 NFL season, several teams had success with multi-back rushing systems. The Giants used the combination of Earth (Brandon Jacobs), Wind (Derrick Ward), and Fire (Ahmad Bradshaw). The Panthers used DeAngelo Williams and Jonathan Stewart. The Titans used Smash (LenDale White) and Dash (Chris Johnson). All three of these teams ranked in the top seven in yards per carry and each earned a first-round bye in the playoffs. For these squads, and others, splitting carries may have been a factor in their rushing achievements.

Some NFL analysts claim that having a system that uses multiple backs increases the explosiveness of a running game. I wanted to see if the stats backed this up.

I attempted to find the connection between explosiveness and rushing system in 2008 by analyzing every team game-by-game and seeing how the percentage of carries given to the primary running back (degree of single-back system) correlated to yards per carry for the team (running explosiveness).

From this analysis I could have gotten one of three possible outcomes.

1. Multi-back systems led to more rushing explosiveness in 2008.

2. The Giants, Panthers, and Titans were aberrations, and single-back systems were actually more explosive in 2008.

3. There was a weak correlation between the type of running system and the explosiveness of the ground attack in 2008. This would mean that the system employed might not have been a factor in a team’s yards per carry.

 II. Data Collection

The two main variables utilized are rushing explosiveness and degree of single-back system. I used yards per carry to represent running explosiveness. I used the percentage of carries given to the No. 1 running back to represent the type of system.

To clarify, let’s say the Chargers rush the ball 30 times in a game for 120 yards. The yards per carry would be 4.0. Let’s assume LaDanian Tomlinson had the most carries for San Diego in that game with 20 rushes. The percentage of carries given to the primary back for that game would be 67%.

I used game-by-game statistics to be more exact. I didn’t use cumulative season statistics because the percentage of carries given to the primary back over the course of a year is not always representative of the team’s rushing system.

For instance, in 2008, the Colts appeared on paper to have more of a split-back system than they actually had. Over the course of the season, 42% of the carries went to the running back with the most carries overall (Joseph Addai). This percentage is much lower than the league average and makes Indianapolis look like it has a multi-back running strategy. In actuality, the Colts used much more of a single-back system. Addai was the starter, but when Addai got hurt, Rhodes stepped in as the No. 1 back. Upon Addai’s return, the two split carries, but only for a few games.

For the majority of the season, the Colts were a one-back team. But, at the end of the season, Addai had only three more carries than Rhodes, and the statistics make it seem like the system was perfectly split. When looking at the Colts game-by-game, you can see that they actually gave their primary running back the ball 71.4368851% of the time. This is higher than the league average.

In the NFL, teams gave their primary running back the ball an average of 63.5% of the time during a single game. I listed the statistics for every NFL team in 2008 below.

Team	YPC	Percent carry No. 1 back
Giants	5.01593625	0.547414371
Falcons	4.83531746	0.680295648
Panthers	4.81136951	0.568452033
Ravens	4.77572559	0.530822269
Vikings	4.74881517	0.707514804
Patriots	4.49325626	0.4243376
Titans	4.44054581	0.551510872
Redskins	4.38284519	0.722403218
Jets	4.3625	0.697343108
Raiders	4.32897603	0.601846406
Dolphins	4.32874016	0.503106164
Broncos	4.2967581	0.517222131
Texans	4.27314815	0.637226573
Bills	4.23980815	0.638919522
Bucs	4.234375	0.564201699
Chiefs	4.19589977	0.634282602
Packers	4.16431925	0.721976882
Jaguars	4.13043478	0.544984478
Seahawks	4.09976247	0.57532055
Chargers	4.07317073	0.718190183
Cowboys	4.02770781	0.720021806
Eagles	4.01351351	0.653677201
Steelers	4.00502513	0.663836205
Bears	3.97423888	0.740827297
Rams	3.95443645	0.741879066
Browns	3.92420538	0.680018854
49ers	3.85483871	0.701949551
Saints	3.78409091	0.559673326
Bengals	3.67391304	0.67946476
Lions	3.61904762	0.743780707
Colts	3.46470588	0.714368851
Cardinals	3.44324324	0.641194996

III. Results

After I compiled the data, I ran the regression. There was a negative correlation between the percentage of carries given to the primary back (degree of single-back system) and running explosiveness (yards per carry). What this means is that the more a team split carries, the higher that team’s yards per carry was in 2008.

The least-squares regression line turned out to be…

yards per carry= -1.922714(percentage carries to primary back) + 5.407991.

For every tenth of a percentage point decrease, a team got .1922714 more yards per carry.

The correlation was not overwhelming, but it was definitely not negligible. The correlation was -.4174925149. Also, the 95% confidence interval for the slope (-3.48291, -.3625175) included all negative values.

Out of the 16 teams with the highest yards per carry during the season, 12 were below the median for percent of carries given to the primary back.

It appears that multi-back teams did indeed have more rushing explosiveness in 2008.

Jake is a sophomore in Currier House. He is concentrating in Economics and pursuing a secondary field in Government.