NFL fans have spent decades arguing over whether a particular player is injury prone. Some view the NFL as a violent league where everyone is at risk of injury on every play; those players who actually go down with an injury may simply be victims of bad luck. Others argue that certain running backs are simply more injury prone than others - although most agree that some players start out as injury prone and then end up becoming very durable. One might claim that being an every-down, every-game running back wears on a player, and that it's easier to look good with a lighter workload.

Fantasy football is a complex game. But sometimes, I just want to see how a player performed when he actually played. The more specific you can get, the better, and I like gauge a player's fantasy potential before worrying about injuries.

I looked at all running backs who ranked in the top 50 in fantasy points in 2011. I then noted how many quarters each of those running backs played in 2011. I included overtime quarters, so it's theoretically possible for a running back to play in more than 64 quarters, although none did last season. If the running back had at least one rush attempt or one target in a quarter, he gets credit for playing in that quarter. But if a player was injured early in the first quarter, his production in that game will in essence be divided by just one-fourth of a game instead of a full game. By using a more granular approach to per-game numbers, we can really see which running backs played well in 2011 -- at least, whenever they were on the field. The table below shows each running back's fantasy points in 2011, number of games played, number of quarters played, fantasy points per game, fantasy points per game, and the running backs' ranks among the 50 RBs in FP, FP/G and Fantasy Points per Four Quarters (FP/4Q).

Which players stand out as potential fantasy sleepers?

You might be surprised to learn that Lions running backs last year ranked 13th – as a group – among all NFL teams in fantasy points last year. After six weeks, Jahvid Best ranked 9th in fantasy points. Best ended the year 8th in fantasy points per game, and Kevin Smith was 7th in fantasy points per quarter. For obvious reasons, none of the Lions running backs are being drafted as starters in 2012. Smith has the highest ADP at RB38, Best is right behind him, and Mikel Leshoure is at RB45. Considering the ridiculous pass/run ratio the Lions had last year, the fact that the group was still productive when healthy means it is likely that one of Smith, Best or Leshoure will have legitimate fantasy value in 2012. Smith seems to be the safest option, but may have the lowest upside. In any event, Smith seems likely to be a good option early in the year while Best and Leshoure aren't on the field.

Darren Sproles and Chris Johnson were compilers last year, as both played in nearly every quarter in 2011. Sproles ranked 6th in fantasy points, but only 16th in fantasy points per quarter; that's more in line with his RB18 ADP. On the other hand, Chris Johnson ranked 20th in FP/4Q last year, but 12th in fantasy points. Fantasy owners must have 2009 on the brain, as Johnson currently is the first running back drafted after the big three of Adrian Foster, Ray Rice and LeSean McCoy. It may be tempting to say "if Johnson can rank 12th in fantasy points during a down year, where will he rank if he improves?" But it's more appropriate to consider him as ranking 20th last year but staying healthy, which means he'll need to significantly improve to merit a top-seven draft pick.

Fred Jackson ranked 4th in both fantasy points per game and per quarter, but his ADP is only RB15. Obviously C.J. Spiller is expected to take on a larger role, but I view Jackson as a steal at that price.

Shonn Greene doesn't have a lot of juice, but he ranked 25th in FP/4Q while LaDainian Tomlinson was a big part of the offense. Greene currently has an ADP of RB22, which is a very small bump for a player who may be in line for significantly more carries in 2012. If you don't believe in Joe McKnight and Bilal Powell, then Greene should be a value pick.

Ahmad Bradshaw was a strong RB2 in 2010 and again in 2011, ranking 13th in FP/4Q. The Giants ranked last in rushing yards and yards per carry last year, but I expect them to rebound a bit in 2012. Swapping Brandon Jacobs for David Wilson might be bad for Bradshaw's long-term prospects, but he seems undervalued with an ADP of RB17.

I like Frank Gore, but he was in an ideal situation last year as the 49ers often played with a lead. Still, he ranked only 21st in FP/4Q, and now will have to compete with Brandon Jacobs, LaMichael James, and an improving Kendall Hunter. With an ADP of RB19, I'm not sure if Gore has enough upside to justify taking him there.

Questions, suggestions and comments are always welcome to stuart@footballguys.com.