Non PPR league and I currently have L Murray slated as my RB2. If I'm playing match ups, Philly's D is susceptible to screen passes and outside runs, but I don't think the Cowboys use Dunbar as heavily this week after having a week to game plan for Bryant's absence.
Over L. Murray no. Flier maybe who else is on your bench? They did have time to plan without Dez, but that will be part of the plan. The rock will get spread out Dunbar will be part of that.
PPR, yes, worth an add. No PPR, not worth looking at unless you're incredibly desperate - which you aren't, or shouldn't be, having Murray.
In PPR I typically prefer to ride with a receiver at Flex, but Sankey isn't terrible. I have him at 72 this week. In regards to Dunbar- it really depends on your entire team makeup.
