Two running back situations have rocked the Fantasy world this week: Kevin Smith went from out-of-the-NFL to the Lions' starter in three weeks time, and Fred Jackson will miss the rest of the season with a fibula fracture. What does it mean for this week?

Let's start with Smith, who looked fantastic last week as he throttled the pitiful Panthers run defense for 201 total yards and three total touchdowns. While doing that he proved to the Lions coaches that he can deliver the versatility, speed and even pass protection skills they've been desperate for since Jahvid Best went down. Don't forget that as a rookie he led the Lions with 1,262 yards and eight touchdowns in 12 starts before struggling and getting hurt in 2009. Best is still sidelined -- who knows if he'll return this year -- and Maurice Morris will probably accept a role as a change-of-pace back. The team is desperate to get their run game going to take some pressure off of Matthew Stafford. Just like that, Smith has snared a rare 20-touch job.

Now he'll take on a Packers defense on Thanksgiving that has allowed a rushing touchdown in four straight games and a running back to top 100 total yards in three of their last four. The timing is right and the matchup is favorable for Smith to at the very least be productive. How about 201 total yards and three touchdowns? Won't happen. But if he gives you a third of that, you'll be pleased that you started him.

The end of Jackson's season in Buffalo signals a similar opportunity for C.J. Spiller to become a big-carry back in Buffalo. But the former first-round pick has been anything but effective through 24 NFL games, totaling 398 rush yards, 239 receiving yards, two touchdowns from scrimmage and a lot of limited action. He's never had more than nine carries in a game, never more than five receptions at once. Why? A combination of never adjusting to the NFL game and not knowing the Bills' playbook has always been suspected. Fred Jackson playing consistently well has also pushed Spiller to the sideline. With Jackson gone, Spiller will be the Bills' top back for better or for worse.

However, this isn't the week to ride him and expect big things. Buffalo's offensive line has fallen apart as multiple starters have been lost for the year, none bigger than center Eric Wood. Additionally, the Bills claimed running back Tashard Choice off waivers and have rookie rusher Johnny White on staff. Both could get in the mix, especially if head coach Chan Gailey still isn't ready to trust Spiller for more than a dozen touches. Choice worked with Gailey while in college at Georgia Tech and White was a fifth-round draft pick by the Bills and has some decent versatility and speed himself. The hunch is that Spiller will start and White will get a crack to play in short-yardage situations. Choice's role is totally up in the air. White is actually an intriguing deep sleeper given Spiller's lack of production.

What's more, the Bills are playing at the Jets, who have started to improve against the run. They've allowed one touchdown to a running back over their last five games (Tim Tebow had one last week, though) with one 100 total yard running back in that span -- Fred Jackson. It would be a huge surprise for Spiller, who has never totaled more than 84 yards in a game in his career, to nick up the Jets.

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