I don't think they're going to just throw Bell in for fun when Griffin has been running well. Any RB is going to struggle against good defenses, but when Denver plays an average/poor defense, he's going to get his yards.
The only way I can see Bell getting in there is if Denver is out of the playoff race. Then they may want to see what he can do. Otherwise, I'd say at this point it's Griffin's job unless he gets hurt.
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