Yards per attempt exact definition?

A lot has been made (mostly by fans of other teams) about Denard's yards per attempt prior to yards after the catch.  Granted, I don't believe have actually had many yards after the catch, so that's not my concern, but I was wondering -- is yards per attempt calculated from where the ball is spotted on the line of scrimmage to the intended target, or is it caculated from the spot the ball is thrown to the intended target?

I realize this may be kind of a dumb question, but I honestly don't know, and the distance from the line of scrimmage back to where the ball is thrown from can vary depending on the depth of the QB's drop.  Could anyone answer this for me?  Thanks.