"Davis is not playing well in practice and is not ready for the toughest part of the schedule."
Ultimately it could be as simple as this. None of us are in practice. Davis might be hitting guys in their shoelaces or floating passes ten feet over their heads. He may have poor practice habits. He might not be learning. He might be a disaster ten times worse than Crane. But, he's all we have. The staff has deemed him the next best option after Crane. They want to keep Tuggle's redshirt. Crane's play dictates that you try something else.
Even if Davis is the worst practice player ever with a thin understanding of the offense, you take a shot. Some players perform differently when it is game time. Some rise to the occasion. Plus getting him out there forces the other team to adjust and prepare for two QBs. Even if the staff thinks he is terrible, Clemson, Notre Dame and Maryland don't know that. They just see another tall athletic QB across the line.
If Davis gets out there and looks terrible or turns the ball over, you put him back on the bench. One turnover is not going to be anything worse than the mistakes that Crane has made.
Later in the week I'll get into the Crane upside argument.