Last year, Football Outsiders developed BackCAST, a metric that projects the likelihood of success for running back prospects in the NFL draft. Historically, a college running back with a good size-to-speed combination and high average yards per carry and who represented a large percentage of his college team's running attack is more likely to succeed at the pro level. BackCAST considers these factors and projects the degree to which the running back will exceed the NFL production of an "average" drafted running back during his first five years in the NFL.
For example, a running back with a +50 percent BackCAST is projected to gain 50 percent more yards than the average drafted running back. BackCAST also projects whether each running back is likely to be heavily involved in the receiving game or is more of a ground-and-pound back.
This year, BackCAST suggests we have an amazing 2017 class of running backs. Indeed, not one, not two, but three running back prospects would make the list of the top 10 prospects ever in BackCAST's database (since 1998). This class also boasts a high number of strong midround prospects, making this the ideal draft for a team with a need at the halfback position.
For an explanation of how BackCAST works, check out the full detail at the bottom of the article.
What follows is a ranking of the top running back prospects for 2017 according to our model, as well as one fairly highly regarded prospect whom the model suggests as a likely bust:
1. Leonard Fournette, LSU
BackCAST score: +142.2 percent
Type of back: Balanced
Similar historical prospects: Ricky Williams, Willis McGahee
Fournette has an amazing size-and-speed combination. The average drafted running back is 216 pounds and runs a 4.55 40-yard dash. Fournette, by contrast, is faster than the average running back at 4.51 seconds and much heavier at 240 pounds. (He dropped to 228 pounds at his pro day, but unfortunately for football analytics enthusiasts, he did not run the 40 again.)
Fournette was also no slouch when it came to collegiate production. In his career, he had significantly more rushing attempts than the typical prospect, even though he missed a good third of his junior season because of injury (and also, perhaps, because of a desire to preserve his health for the draft). Fournette also averaged more than 6.2 yards per attempt in his career.
Teams are right to hesitate before using a first-round pick on a running back, but Fournette's numbers are so good that it's hard to argue that teams at the top of the draft who have a need at running back should pass on him.
2. Dalvin Cook, Florida State
BackCAST score: +136.0 percent
Type of back: Receiving
Similar historical prospects: LaDainian Tomlinson, LeSean McCoy
Talk about a consolation prize. A team that misses out on BackCAST's top running back needs only to settle for another one of the best projected running backs of all time. Cook's projection is so high because he sports an unusual combination of usage and efficiency. When a college running back is the focal point of his team's offense, opponents will scheme against him. Although the running back can still be efficient, it takes a unique talent to post peak-efficiency numbers while carrying an unusually large load.
There have been plenty of running backs who have been used as heavily as Cook or have been as efficient as Cook, but only one running back ever who has been both. Other than Cook, Ricky Williams is the only RB prospect ever to score an AOEPS (BackCAST's metric for measuring the degree to which a running back prospect dominated his college team's backfield) above 20 percent while also gaining more than 6.0 yards per attempt.
You could make a case for drafting Cook over Fournette, the top-ranked prospect. Although Fournette has an awesome projection, his particular profile somewhat matches other running backs who boasted great projections but ultimately disappointed. BackCAST also was high on Ron Dayne and T.J. Duckett, for example, who scored highly in large part because of their unusual size-speed combinations. It is a bit harder to find a bust whose high projection, like Cook's, had more to do with college production.
Also, Cook has strong receiving potential, which means that even if he does not succeed as a traditional back, he'll probably have some value as a Reggie Bush-type who can catch passes out of the backfield.
3. Joe Mixon, Oklahoma
BackCAST score: +115.7 percent
Type of back: Receiving
Similar historical prospects: Edgerrin James, Darren McFadden
Of course, we strongly condemn the off-the-field actions of Mixon. BackCAST, however, is a mathematical construct that does not make any moral judgments and has no way to factor in the effect of a prospect's off-the-field actions.
If nothing else, BackCAST's positive outlook on Mixon's talent is a testament to the potential he has squandered. He was not quite as heavily used as Fournette or Cook, but he was more efficient, averaging more than 6.7 yards per carry, the highest of any running back in this year's class. Mixon was also a prolific receiver, and he therefore projects to be the second-best receiving back in this class.
4. Brian Hill, Wyoming
BackCAST score: +84.6 percent
Type of back: Balanced
Similar historical prospects: Marshawn Lynch, Michael Turner
Hill is a major BackCAST sleeper who could potentially be had in the fourth round or later. Indeed, Hill's strong BackCAST projection would theoretically put him on top if he were part of a weaker draft class.
Hill's 4.54-second 40-yard dash is average for a drafted running back, but he's a big back at 219 pounds, which gives him a good size-speed combination. Wyoming used Hill heavily, and his AOEPS is better than that of any other running back in this class, save for Cook. Hill's biggest drawback is a lower average of 5.53 yards per attempt, although that is not unusually low for a running back with a workload as heavy as Hill's: 1,860 rushing yards on 349 carries and 22 touchdowns in 2016.
5. Marlon Mack, South Florida
BackCAST score: +80.8 percent
Type of back: Balanced
Similar historical prospects: Melvin Gordon, Ryan Mathews
Although not quite the sleeper that Hill is, Mack could be a pleasant surprise for a team that spends a midround pick on him. Thanks to a strong freshman season, Mack posts a good AOEPS. It is hard to say whether AOEPS underrates or overrates him.
As his career progressed, Mack ceded carries to running quarterback Quinton Flowers, but he also lost carries to fellow running back D'Ernest Johnson. Mack also posted a strong 6.2 yards per carry, which, combined with his good AOEPS, makes him a sort of discounted Dalvin Cook.
6. Christian McCaffrey, Stanford
BackCAST score: +76.2 percent
Type of back: Receiving
Similar historical prospects: Reggie Bush, Jacquizz Rodgers
Typically, when a first-round running back prospect comes in sixth on BackCAST's list, it's time for an explanation about why the prospect is overrated. McCaffrey, however, is simply a victim of being "only" an average first-round prospect in a draft full of historically great prospects and strong sleepers. McCaffrey's projection suffers a bit because he had few carries as a freshman and lost carries to Bryce Love as a junior.
Overall, McCaffrey is a strikingly similar prospect to Mack. McCaffrey has much better receiving numbers, but Mack edges him slightly in AOEPS and size-speed combination. In fact, the best reason to draft McCaffrey is his receiving potential. McCaffrey is light and was prolific in the Stanford passing game, which gives him the highest receiving potential in this class.
7. Samaje Perine, Oklahoma
BackCAST score: +72.9 percent
Type of back: Ground-and-pound
Similar historical prospects: Jonathan Stewart, Laurence Maroney
Perine is a good sleeper for a team looking to flat-out pound the ball. He is rather slow, with a 4.65-second 40-yard dash, but he is an absolute load at 233 pounds. Perine somehow managed to post a nice AOEPS despite having to share the backfield with Mixon during his sophomore and junior seasons. That freshman season, however, was particularly impressive: Perine ran the ball 263 times for 1,713 yards, an average of 6.51 yards per attempt.
One could only imagine what Perine's college numbers might have looked like if Mixon hadn't been on the roster. Perine is not particularly explosive in the passing game, never posting more than 108 yards receiving in a season, and thus projects as a ground-and-pound back.
Potential bust alert
Alvin Kamara, Tennessee
BackCAST score: -30.4 percent
Type of back: Receiving
Similar historical prospects: Julius Jones, Montario Hardesty
Kamara is not a hopeless case, but it is unusual for a player with this many holes in his BackCAST projection to be rated as a second-round pick by scouts. Kamara had trouble getting carries for the Volunteers. It would be one thing if Kamara had been stuck behind a particularly talented teammate, but the available evidence does not suggest he was permanently locked in some sort of Thurman Thomas/Barry Sanders situation (both played for Oklahoma State at the same time).
Kamara was the clear second running back behind Jalen Hurd as a sophomore (though, in fairness, Hurd was considered a possible future high-round draft pick at the time). During Kamara's junior year, Hurd battled injuries and his production cratered, resulting in an abrupt decision to transfer from Tennessee. Even with Hurd out of the picture, Kamara barely edged out sophomore running back and former three-star recruit John Kelly for carries.
It certainly could be the case that Tennessee's coaches failed to realize what they had in Kamara and that his NFL career will prove them wrong for failing to give him the ball enough times to star on the field. However, Kelly was actually more productive than Kamara on a per-carry basis, so Tennessee's coaches were not clearly wrong to platoon their backs.
Other signs that Kamara could be a transcendent talent stuck in a bad situation are just not there. He ran a 4.56-second 40-yard dash at 214 pounds, which are firmly average numbers. Kamara averaged more than 6 yards per carry, which is good, but not unusual for a back with relatively few attempts, nor is it a number that makes Kamara stand out among the top prospects at the position.
Kamara has strong receiving numbers, but that should get him only so far. Would teams spend a second-round pick on a player who was going to be the next Travaris Cadet?
How BackCAST works
BackCAST is based on a statistical analysis of all of the Division I halfbacks drafted in the years 1998-2015, and measures the following:
The prospect's weight at the NFL combine.
The prospect's 40-yard dash at the NFL combine. If he did not run at the combine, BackCAST uses his pro day time.
The prospect's yards per attempt with an adjustment for running backs who had fewer career carries than an average drafted running back.
The prospect's AOEPS, which measures how much, on average, the prospect's team used him in the running game during his career relative to the usage of an average drafted running back during the same year of eligibility.
The prospect's receiving yards per game in his college career.