Huh? COuld you please phrase that in a 4th grade level for me. I am confused now.

You have to stand back from the actual line if directed to do so.

If, however, there is an offensive player in the "restricted area," and the pass is going to go there, the defender has every right to try to defend the pass, and can then subsequently enter that area.

(Run-on, I know. I'll try to revise it later.)

I am under the assumption (probably because that is how we always do it) that if the line is on the floor, you use it. No player, A or B, is allowed in that area 9except for the inbounder). It is there to allow room for the throw in. It takes the place of the out of bounds line. Once the throw in is complete i.e. the ball being released from the thrower and crossing the plane, the line 'disappears' (for lack of a better word) and the normal boundary lines are used.