At some positions, depth is exclusively a matter of injury. The starter is the starter, and if all goes well, he's always the starter. Peyton Manning doesn't come off the field in certain formations. The Chiefs don't spell Willie Roaf on some plays or take him out for a series to keep him fresh. Evaluating those positions is about ranking the starters first and foremost, then making small adjustments based on the quality of the backups and the likelihood that they will play.
The same is not true for running backs. Herm Edwards wants the Chiefs to run the ball more than 500 times this year, and no team had fewer than 360 rushing attempts in 2005. 350 carries is heavy use for a single back. That leaves a lot of work for the rest of the depth chart. Add in the increasing number of teams that use a running back committee rather than a clear first-string starter, and it's clear that when ranking the NFL's 32 teams on their running backs, you have to consider more than just 32 players.
These rankings started with the productivity of each team's halfbacks in 2005 and then were adjusted subjectively for things like age (the cruel reality of the NFL, especially for running backs), the quality of fullbacks, and the likelihood of improvement or decline. Teams like the Giants, Falcons and Cardinals (including Edgerrin James) would top the charts based on last year, but they all rely heavily on aging backs likely to pull either a Curtis Martin — an injury-plagued season after a career year at age 31 — or a Marshall Faulk — a slow decline after a consistently productive career. The teams that top the rankings below have great starting backs who are relatively young and durable, with good players available behind them — and ideally great fullbacks in front of them.
You'll see a lot of stats you recognize here, and a couple you may not: DPAR, or Defense-adjusted Points Above Replacement, and DVOA, Defense-adjusted Value Over Average. Both stats take every single play during the season and compares it to the league average based on situation and opponent, rewarding players for strong performance on third down and in the red zone and giving them less credit for meaningless gains like a nine-yard catch on third-and-12. The difference: More DPAR means a running back with more total value, while a higher DVOA means a running back with more value per play. This page lists these advanced stats for all running backs in 2005, both rushing and receiving.
3. Washington
The Redskins may be a surprising choice at third, but they belong in the conversation with their neighbors in this list. Only five running backs posted more DPAR last year than Clinton Portis, and he is younger than any of them. After his rocky first year in Washington, Portis appears comfortable in Joe Gibbs' one-back offense. Last year, according to the Football Outsiders game charting project, only the Colts and Patriots ran behind a fullback less often than the Redskins. Ladell Betts and Rock Cartwright work well as change-of-pace backs — Cartwright in particular deserves more playing time — although neither has the all-around talent to really take over for Portis should he suffer a major injury.
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