ESPN's Dan Graziano broke down the Giants RB situation and said he expect the Giants' run game to lean heavily on Rashad Jennings in the early going, with rookie Andre Williams serving as the primary backup while Williams gets up to speed.
He added he's curious what happens when they get close to the goal line? Will they stick with Jennings or switch up to Williams or Peyton Hillis for the dirty work? Jennings can surely handle it, but if they're asking a starter's workload of him otherwise, they may assign the goal line banging to Hillis for the sake of preserving Jennings and/or Williams.
It's also possible the Giants will throw more in the red zone than they did under their previous offensive coordinator, though they're not exactly loaded with classic options at red zone receiver or tight end.
But as far as the workload, I think Jennings is the bell cow to start and Williams has to play his way into more carries. I think he's capable of doing so, and that he's excellent with the ball in his hands. But in order to truly eat into Jennings' snaps, Williams is going to have to show he can reliably catch the ball and pick up the blitz in pass protection.
It's a typical reason why rookie RBs don't often get a lot of time early in the season or more specifically on passing downs - blocking in pass protection. Williams has struggled a bit, as well as pass catching, in camp according to reports, so right now Jennings looks like the guy who is going to get a bulk of the work - at least early on.