Fed Rules:

When the center snaps the ball, it hits the center in the leg. The ball then falls to the ground. The ball never touches the QB. Is this a snap infraction?

Not normally. If it appears that this was a planned play then you definitely have a foul if R wasn't informed. The snap started when the snapper moved the ball and it ended when it hit the ground. I would let go the fact that the snap touched an A lineman's leg, the snapper, and just call it a fumbled snap.

2-38
ART. 1 A snap is the legal act of passing or handing the ball backward from its position on the ground.
ART. 2 The snap begins when the snapper first moves the ball legally other than in adjustment. In a snap, the movement must be a quick and continuous backward motion of the ball during which the ball immediately leaves the hand(s) of the snapper and touches a back or the ground before it touches an A lineman.
ART. 3 The snap ends when the ball touches the ground or any player.

thanks for the reply.

What confuses me is Art 3:
Does the snap end when it touches the center's leg?

NCAA: once the ball leaves the snappers hands, it is a backward pass, live ball, and can be recovered or advanced by either team (exception: planned loose ball foul).

As long as its a continuous motion with the hands, touching the leg has no bearing.