Every year there is one lower tier rookie that tears it up during the preseason, usually destroying defenses and scoring a few TDs. This usually causes a huge bump in cards that shouldnt really be worth what they are, mostly because people dont realize the role the player will actually have during the regular season.
In 2007, David Clowney was the guy, as he had a large role during the preseason, but didnt have a chance of doing anything during the regular season. His cards were going for a ton more than they should be, until people realized that investing in a guy that wouldnt catch a ball during the real games was a horrible idea. He was picked up by the Jets, but didnt put up a single stat in 2007. In 2008, he caught one pass during the regular season. The lesson? Dont let preseason numbers fool you.
This year, running back Glen Coffee has put up impressive preseason numbers. With Frank Gore in the backfield taking most of the important carries, Coffee will get some time, but not as much to make his cards go for what they are right now. Coffee showed he has some talent, but as a third round pick behind a player with a huge contract, it is really tough to put any money behind him without first letting the games play out.