There were many, many quality running backs in the 2008 season, and looking ahead to 2009, there are many, many potential fantasy running back studs. Which of these many potential studs will be actual studs? Frankly, I think that's mostly guesswork and luck, which is why I wouldn't use a first round pick on a running back (maybe not a second round pick, either).* If you saw DeAngelo Williams coming in 2008, bully for you (I wrongly saw him coming in 2006 and 2007). Some of these guys will be bums, and some will be studs, and I can barely guess which will be which (not that I'd tell you what my guesses are anyway).
What I will tell you is what statistical criteria I use to evaluate running backs. I'll use Adrian Peterson's statistics as an example of what I look for.
1. games with 100+ yards from scrimmage
Total yardage numbers can be deceiving; it is important to examine game logs. Consistency matters, especially with the Hazelweird League's cross country scoring (far superior to head-to-head standings: see here and here. I will develop this point again this summer). I want to see see how many productive fantasy games each player has. Adrian Peterson had 100+ yards from scrimmage in 11 of his 16 games, meaning he's a very reliable fantasy running back (he actually had 75+ rushing yards in 15 of 16 games). He's always going to get you points, and he's often going to get you a lot of points.
This number is probably the most important number I look at. It tells me who is regularly getting quality fantasy production, and who is producing too many damaging dud games (0-2 points). You can also check game logs to see how many games the player scored touchdowns in.
2. rushing yards
Totals do still matter. Peterson's league-leading 1,760 rushing yards tell us he is a stud running back.
One reason running backs are great fantasy football producers is because they can contribute points with receiving yards, too. A running back's receiving yards may fluctuate based on a variety of factors; however, if a running back has a lot of catches, that tells me he's a targeted receiver in his team's offense. A lot of receptions means a lot of opportunities to add fantasy points with receiving yards and receiving touchdowns. I like to see a starting running back with at least 40 receptions, preferably 50+. There are two reasons I like running backs with a lot of receiving yards. First, they have a better chance of providing you monster weeks (say, 150+ yards from scrimmage and 2 TDs). Second, they are more consistent: even when they have terrible rushing days, they can still end up getting you solid fantasy production.
Peterson was mostly a nonfactor in the passing game for the Vikings last season, catching 21 passes (Chester Taylor had 45 catches for 399 yards and 2 TDs--I do think it's possible that at some point those receiving numbers will be Peterson's but I don't think that will be 2009). That's the one thing that turns me off of him: I'd rather my #1 RB be a productive pass catcher.
4. yards per rush
Very few fantasy leagues award points for yards per attempt, so why do I bother looking at it? It's simple: a running back with poor or average yards per attempt relies on his teammates and on situations to get good fantasy numbers. A running back with high yards per attempt can make things happen on his own. Adrian Peterson averaged a beefy 4.8 yards per attempt. He's going to be a productive running back.
5. yards from scrimmage
Again, total numbers do matter, and yards from scrimmage is a better indicator of a running back's fantasy production than rushing yards. Adrian Peterson led the league with 1,885 yards from scrimmage, but that was mostly because of his exceptional rushing total.
Notice what I'm not looking at: touchdowns. The Hazelweird League awards six points per touchdown and one point per 20 yards rushing/receiving, so it's not that touchdowns aren't important. Why am I ignoring them? I explain why in detail here, but the theory is simple. I think touchdown numbers can be a distraction: good fantasy players are going to get touchdowns, and other numbers can do a better job of telling me who is a good fantasy player. By ignoring touchdowns, I might find holes in the conventional wisdom, discovering some overrated and underrated players.
*The Hazelweird League is returning to its Auction roots, which makes deception and subterfuge an utter necessity. Everything I say about fantasy football may be a lie. But that doesn't matter: I'm proposing ideas, and it's the idea that's worth considering, not whether or not I believe it or not.