More than most positions in the game of professional football, rookies can make immediate and substantial impacts at running back. Their fresh legs get them though holes and around the ends, and those young knees can make cuts that won't be possible in a few years. Their bodies haven't been abused by 3-4-5 seasons of taking on defenders often much larger than themselves. Just think about the impact James Starks, a sixth-round pick last year out Buffalo, made for Green Bay, and in just four games, during the Packers' recent Super Bowl run.

Running backs have the shortest average pro careers, so teams might as well try to get what they can out of them while they 're young. Discerning which ones could produce coming right out of college is the task of the scouting departments. Combining that with what a team's already got, and making a projection is the task of the NFL bettor.

Last year Buffalo made Clemson's CJ Spiller the first running back taken in the draft at No. 9 overall.  And while Spiller only ran for 283 yards on the season behind Fred Jackson, he may get his chance yet, and soon.

LeGarrette Blount was highly thought of but, for various reasons, went undrafted last year. He then proceeded to rush for 1,007 yards for Tampa Bay, and basically in just the last 11 games of the season.

And in between those guys there was Starks.

And remember, the guy who led the league in rushing last year, Houston's Arian Foster, wasn't even drafted when he came out of Tennessee in 2009.

So instant production can come from almost anywhere among young running backs.

Here's a quick look at the top running back prospects for this year's NFL draft (April 28-30), and a few others.

1. Draft guru Mel Kiper compares Heisman winner Mark Ingram of Alabama to Emmitt Smith, one of the best all-time at getting the most out of almost every play, whether it was one yard or 10. Ingram ran for almost 1,700 yards as a sophomore, leading the Tide to the National Championship, but he had knee surgery and missed the first two games of last season, running for 900 yards after that. He’s not flashy, just very solid. He will be the first RB taken, and Miami would probably love to have him.

2. Mikel LeShoure powered his way to a new season rushing record at Illinois with almost 1,700 yards last year. He is a bit of a load at 6-0,/230, likes contact, and can make the first guy miss. Like Ingram, he is leaving school a year early. 

3. Ryan Williams ran for 1,650 yards as a freshman at Virginia Tech, but a bad hamstring limited him to 500 yards last year, and those are his only two college seasons. Williams was very dangerous in 2009, with many big runs, bursting away from defenders.

4. DeMarco Murray of Oklahoma fought though several injuries to pile up 5,200 yards from scrimmage and score 63 touchdowns in four years with the Sooners. A good receiver out of the backfield, but his upright running style causes concern. Better learn to secure the ball, too. Murray has been compared to Reggie Bush.
 
5. Jordan Todman ran for 2,800 yards his last two seasons at UConn and is also leaving as a junior. The knock on him, though, will be his size at 5-9,/190.

Realistically, any of the last few on the above list could be grouped in with another half-dozen or so prospects, guys like Daniel Thomas of Kansas State, a former JUCO quarterback who ran for 2,800 yards in two seasons with the Wildcats; Delone Carter of Syracuse, who's tough inside style has drawn comparisons to Marion Barber; Shane Vereen of Cal, who's been compared to Ray Rice; and Kendall Hunter of Oklahoma State, another smallish/stoutish runner who put up two 1,500-yard seasons with the Cowboys.

It might be a bit hard to believe, but there might not be a running back taken in the draft until Miami comes up at No. 15. Every team above that either already has a main ground-gainer and/or more dire needs at other positions. After the Dolphins the next team in real need of a running back might be New Orleans at No. 24. And New England has two first-round picks, at 17 and 28, and the first pick of the second round, so they might be tempted to grab a RB at one of those spots. Beyond the first round is anybody's guess as to who might take who.