Dallas will run this from the I and from a split back set. Here, they go full (split) with Tony Romo in the shotgun. The spread look has the Redskins playing man under with two deep safeties and a base 3-4 look up front. From this set, the back will shuffle laterally until he's even with the centers left leg, then take the ball to the 20 gap over the right guard. The play side linemen will fan or block the defenders outside of them. Tyron Smith gets OLB Ryan Kerrigan and RG Kyle Kosier blocks the DE lined up over Smith. Center Phil Costa takes on NT Barry Cofield head on, and the F-back John Phillips goes for the first LB on the play side from the center out. In this case, that's London Fletcher.
You can see the four outside Cowboys linemen, the Gs and OTs, get outside turns. Phillips is heading for a collision with Fletcher and Murray may have a lane on the right side:
He doesn't in this case, because the center is beaten quickly:
Murray has not running lane, and breaks the run left, where he's dropped for a two-yard loss.
This play can be effective and has been effective when the passing game has excelled. These stills demonstrate why the Cowboys running game has run cold then hot all year. It only takes one missed block to sabotage a play.