OK... I am stupid about this but can someone explain to me why you cannot just make Rex a QB for the game? If Green went down last week could you make a roster change and have Rex (or someone else) play QB... I'm assuming this is first grade stuff, but for the life of me I dont know...
I'm not a coach so I don't know the entirety of the reasons, but from my perspective there are a few big ones.
1. Rex doesn't know the plays from the quarterback position. He knows his base package of wildcat plays, but since he is in fact a runningback, he's taught a runningback's role. He has no clue how the reads, progressions, audibles and etc. work from that position on the field.
2. It completely takes away our passing game, so teams can pin their ears back without having to worry about it. Rex was a quarterback in high school, sure, but it takes so much more than you think to be able to throw a decent ball in the college game. Look at Cody Green, he is a D1 caliber quarterback and still has a hard time completing passes that, to the fans, seem simple and easy. Imagine how much worse Rex would look throwing those balls.