I'm not a big fan of the thinking that the running game is all in Callahan's department, and thus all the blame lies with him. Gruden is the HC, and our run game was a disaster last year. Not bad. Not really bad. Titanic-level bad - disaster-level bad. Frankly, I don't give a shit who is calling the plays, designing the gameplan, whatever. I want better results than what we saw last year.
Ultimately, that's on the Head Coach. He and his apologists can blame Callahan, that's fine, IDGAF. But if Callahan is that bad, fire the guy. If he is the reason we can't get a running game going worth a shit, can his ass.
The running game was a disorganized, monkey-throwing-darts mess last year. There was no rhythm or semblence of a plan associated with it. Within the coaching staff, that may be on Callahan. But ultimately, Gruden has to look at Callahan at some point and say, "WTF dude? Either get it done or I will". And he did not do that.