Our fourth look at CBS Sports' Pat Kirwan's recent article addressing what it means to have depth in the NFL, we move away from the offensive line and instead, take a look at the running back position. Kirwan developed 13 questions, looking at key positions on the field and who would fill in if needed. In the end, Kirwan found that the defending Super Bowl Champion Seattle Seahawks and the Cincinnati Bengals best fit the idea of "depth" on a roster.

In his "honorable mention" list, Kirwan placed the Washington Redskins, Tampa Bay Buccaneers, Miami Dolphins, and a "tossup" between the Philadelphia Eagles and San Francisco 49ers. Explaining how the Dolphins, and the other teams, landed on that list, Kirwan wrote, "they don't satisfy all the categories but they did better than most teams hitting on at least nine of the 13."

Since the Dolphins met the entry criteria for the depth discussion by having a backup quarterback that "can go at least 2-2 in a four-game stretch" with Matt Moore, the next question on Kirwan's list is:

Is there a quality second running back that can deliver a 100-yard rushing day if he had to start?

This is a yes at this point. Miami has three running backs who are capable of gaining 100 yards, led by Lamar Miller and Knowshon Moreno. Miller has one 100-yard game in his career, while Moreno adds three with four games over 90-yards. Although many Dolphins fans will be reticent to admit it, Daniel Thomas is also capable of rushing for 100-yards if needed, with two career games hitting that mark, and another over 90-yards.

While none of these three seem to be dominant runners, who are going to tally huge chunks of yardage each week, the change in Miami offensive schemes may be exactly what the running back group needs. New offensive coordinator Bill Lazor should commit to the run, especially compared to Mike Sherman's offense last year that almost seemed afraid to try to run the ball. Add in a revamped offensive line, which should provide a huge upgrade in run blocking compared to last year, and any of the three could break out a 100-yard performance if needed.

The Miami running back group may not be the greatest trio of running backs assembled, but they should be considered to have decent depth where, if something were to happen to one of the three, the other two could provide prodcution in the starter's absence.

That would be the defintion of depth, and would answer Kirwan's question.