Delay of game?

[bigwes68]

Toward the end of the Tennessee-Vanderbilt game today, Tennessee attempted to spike the ball to stop the clock with less than :20 to play. The ball was marked ready for play, there was a direct hand-to-hand snap, and the ball appeared to have been legally spiked. However, right at the snap, the referee dropped his flag, but did not kill the play before the spike. After the play, the referee signaled a dead ball, delay of game.

No one I have talked to has been able to figure out exactly what happened on that play for it to be a delay of game. I might have understood illegal formation or false start because I'm not sure UT's offense was set or had 7 on the line. But why would this have been called delay of game? Is there some special NCAA rule I am not aware of for this situation?