Foster biggest strength is his ability to be patient behind his blocker. With the right side of the O line being atrocious as they are, his biggest strength has become his biggest weakness.
When that side of the line is getting breach at the point of handoff he needs to abandon his patient running and hit whatever hole that is in front of him. Instead he gets chase down by the lineman causing the breach.
That's why Tate and Forset are getting more production per carry. Those two are not as patient and that's why it looks like they getting to the holes faster.
If that right side don't improve it's best to play Forset and Tate. But we all know that'll never happen.
That side of the line is also atrocious on pass-blocking. People blame Schaub for not getting us back in the N.E. game. But it was that part of the line that kept getting blown up and missing blitz pickup that ultimately kill our comeback chances.