Question:
What happens if the quarterback knocks the ball away from the center 
but never actually possessed it?  
Would it be a live fumble, or did the play never start?

Answer:
If the QB touches the ball and at some point thereafter
it falls off the Center, it is a fumble and the first team to touch
the ball has recovered it.

But understand this. If the QB touches the ball then moves the grasper
away from the ball and then a defensive lineman hits the center and knocks
the ball loose, that is an offside on the defense.