If this past weekend has taught me anything, it's don't write off players or teams this early in the season. Pittsburgh came out against two of the league's best team, got hammered, then sat out a bye week. This weekend, they shut down what had been a high scoring Browns offense.
Bettis has faced the #5 and #6 fantasy defenses this year, whose teams also boasted high powered offenses. He has also faced a division rival, which is always an uncertainty. Next week he faces a strong New Orleans defense.
Bettis, in my opinion, remains a #2 RB when the matchup is favorable. By #2 I mean behind any studs you may have. If you have the likes of Ahman Green and Fred Taylor on your team, Bettis is no better than a reserve at any time. If you don't have two studs, then play Bettis when the matchup is favorable.
DeShaun Foster has alot of talent and may develop into a great NFL running back, but it's unlikely that it will happen anytime soon. He has to battle back from injury, overcome a very productive Lamar Smith, and avoid his past problems with fumbles. That's alot to expect of a young RB in his rookie campaign. Scouts questioned his durability going into the draft, and sure enough he's missed games all ready. At this point, you have to consider Foster an injury risk who may not be able to push for the starting job. I like him in a keeper league, but I don't think he'll do much this season until late in the year.
I'm doubtful that Bettis will be your answer for a #2 back, as I only expect him to be productive when the matchup is very favorable, but he may be a step in the right direction if you're having severe problems at that position. Foster certainly isn't an immediate answer.