Right now one of the most confusing RRBC situations in the NFL is in Detroit. While 1000 yard rusher Tatum Bell moved over from Denver, I don't believe he has the starting job all to himself.
First, I don't know how much of his 1,025 yard season last year (in only 13 games) was his talent and how much of it was the Denver system. The Detroit offensive line is a sieve compared to what he had to run behind in Denver. Bell is in for a rude awakening.
Second, there's Kevin Jones. You know, the guy who started 39 games over the past three seasons? He's coming off a serious foot injury, but he recently had two pins removed and he's projected to be ready for the start of training camp. Jones is established and knows the offense. When he gets back to full speed, I expect he's going to get his playing time.
Third, there's T.J. Duckett. Duckett is competing for a starting spot in camp as well and despite five years in the league he's still a bit of an unknown. It's doubtful that he would end up being the every-down back, he's still more of a short-yardage, goal line type of guy. Tatum Bell only had 2 rushing touchdowns last season; somebody has to put the ball over the line. He's definitely in the mix.
Put that together and what do you have? You have a very ugly fantasy RRBC situation. Tatum Bell will likely start off as the speed back, with Duckett finding a lot of playing time as the wrecking ball. As Jones comes back (whenever that is), he'll likely take more playing time from Duckett, but should steal some carries from Bell as well. I expect to see Detroit go with the hot back depending on how the game progresses. Some games fantasy players will see Bell end up with 20+ carries for about 125 yards, some games they'll see Kevin Jones with 20+ carries for 95 yards and a TD. And on any given week, Duckett could vulture a touchdown. Or two.
The safest way to play this right now is to consider Bell the lead guy in a RRBC situation. Don't draft Bell as a #1 fantasy RB, because he's barely a #1 RB on the Lions.