Mac just doesn't make plays. I honestly can't think of a single time this season when he MADE a play. Maybe one of the runs against WVU (pre-fumble).
If the play is there, he will complete it about 50% of the time. If there isn't much there, he'll probably take a sack or throw an interceptable ball. But he never is the reason that something good happens.
I expect with Nebrich or McCummings, our amount of bad plays might increase. I also fully expect that our amount of good plays might increase. The season is a waste, so I would have no issue going Nebrich/McCummings in a timeshare one quarter on one quarter off just to get them time for next year, unless one really establishes himself.