I wrote the NFHS Redding Study Guide writer George Demetriou about this. Simply stated: Once the spot is designated for a free kick along the line of scrimmage and between the hashes the ball may not be removed from that area.
An exception, but a tight one, is the removal of a ball from a tee for a drop kick but it must be in nearly the exact spot of the tee on the free kick line to be legal or its a free kick infraction. Free kicks (other than a Safety) may be a drop kick, from a tee, from the ground or tee while controlled by a holder all at the designated spot on the free kick line (normally the 40), or on a Safety free kick only, be punted within one yard of the line.
The ball may not be kicked off the ground while it is simply laying there next to the tee or a kicker acts like he's picking it up and kicks it. The drop kick needs to be clear, or the ball clearly set on the tee, or controlled by a holder either on the tee or ground for a free kick to be legal or it's Illegal Kicking.