Whenever he's drafted, Shonn Greene will probably eclipse William Green

No one's too likely to get very bent out of shape if Iowa's Shonn Greene isn't taken in Saturday's NFL draft until late in the second round.

At least they shouldn't be.

History tells us a lot of terrific running backs were undervalued in past drafts, while others were overvalued.

Look back to 2002. The first running back taken in that year's draft was William Green with the No. 16 pick, by Cleveland. Green had a nice rookie season with 887 rushing yards, but got into legal and substance-abuse trouble. He never equaled his first year in the NFL, and was out of the league by the end of training camp in 2006.

In that same '02 draft, Clinton Portis was picked 51st, by the Denver Broncos. Portis has six 1,000-yard rushing seasons in seven years, with only injury depriving him of a seventh. He has 72 touchdowns, and is still one of the best in the business at his position as a Washington Redskin.

Brian Westbrook of the Philadelphia Eagles was the No. 91 draftee in '02. T.J. Duckett, meanwhile, went 18th. Duckett has been a role player his entire career. Westbrook has 9,330 total yards in his career, three times Duckett's total.

So if Greene is only the fourth or fifth or even sixth running back taken Saturday and is the 50th or 55th or 60th player picked, remember Portis and Westbrook.

Remember Frank Gore (65th in 2005), Marion Barber (109th in 2005), Brandon Jacobs (110th in 2005), Michael Turner (154th in 2004).

Some players will get most of their career money this spring and summer. Others will get theirs a few years from now, for performance rather than potential.