It would probably have to be a quite small circle, they can be bounced around but I doubt they really go that far. Also, I'm fairly certain that they would take damage from being hit that hard.
That being said, it would make for an interesting game of soccer.
I doubt it. First, I don't think lines of Forbiddance are the "3d equivalent" of lines of Warding. Second, they are used as anchors for lines of Warding, so they really shouldn't go moving about on their own. Finaly, they are described as a cross between a line of Vigor and Revocation, not just a 3d line of Vigor.