Why dont the Redskins use audibles?

[SouperMeister]

I heard that on the 3rd and 7 draw, Gibbs gave Campbell the freedom to audible to a pass, but with Philly showing blitz before the snap, Campbell stuck with the call. Philly dropped the linebackers, effectively killing any chance Portis had to score. That said, I like the fact that Campbell was at least given a chance to change the play. Allowing him to run the no huddle against Philly also demonstrates growing confidence that the coaches have in him.