When is a ball snapped in football?
 

I'm involving in an interesting discussion of how offsides Haggans was on the play in the Superbowl where he supposedly induced a hold, wiping out a pass to the one.

My question is when does the 'snap' begin. Is it the milisecond the ball starts moving on the ground or when part of it leaves the ground? If it is the former, I would think that would be incredibly difficult to figure out. It seems to me (though I may be wrong) that refs look to see when a part of the ball is off the ground to determine defensive offsides.

It has to be the movement of the center's hands backwards. That's it.

I highly doubt there is a hard and fast rule however about the ball touching the ground or not.

I guess I mean practically. Because a snap is so quick that you usually aren't exactly sure when the arm/hand moved. It's easier to notice movement of the ball.

As soon as the ball starts to move. Otherwise it is considered an illegal snap.