At running back, the Bucs have two 'sure' things: Legarrette Blount and Earnest Graham. Both players will make the roster. Behind them, a lot of different things can happen. Kregg Lumpkin looked almost certain to make the roster during training camp but has not produced anything during the games, including on third down. Allen Bradford has shown a few flashes, but hasn't looked good either. Mossis Madu and Armando Allen both bring a different style of running to the team, but neither has shown much during the preseason.
A lot of those problems can be blamed on the offense line, but ultimately some of those running backs will have to overcome the offensive line to beat out the guys ahead of them.
Lumpkin is the experienced guy in this position battle. That's not saying a lot, because he has four career regular season carries. That's not a lot of experience. However, he's familiar with the scheme, he's a good pass blocker and a capable pass catcher. His value as a third-down back gives him a leg up, but he needs to show he can run the ball. Ultimately, that's what the Bucs have completely failed to do this preseason. If Lumpkin can show he can run the ball today, he will make the roster. If he can't show that, he could very well lose out to someone who can. It really is that simple.
Bradford is physically very similar to Kregg Lumpkin. His advantage is being a draft pick. His problem is not being a good pass blocker. And his other problem is not having showed much as a runner this preseason. If he doesn't show either running skills, pass-catching skills or pass-protection skills he will probably not make the roster.
Mossis Madu and Armando Allen
Both of these guys are very similar: somewhat productive college running backs who went undrafted and both have the ability to work in the passing game. They bring a different kind of running style than the other running backs on the roster, being smaller guys with a little more shiftiness and quickness. If they can use those skills to produce, even if it is against a third-string defense, the Bucs could decide to keep one of them as a change of pace back.