[Freddy]

Quote: "On the free throw, no one should be in the semi-circle until the free throw is made, missed or ends."

Does "...be in the semi-circle..." mean:
A) lane space player's foot may not break the plane of the free throw line until the ball strikes the ring or the backboard, similar to what applies to the shooter?
B) lane space player may not touch the floor inside the semi-circle (cf. "you are where you were til you get where you're going")?
C) free throw plane is broken by any part of the body stuck out over the free throw line?

I think it's gotta be A).

No help from the POE. It's as blurry as the above explanation, "...the defender boxing out shall not cross the free-throw line into the semicircle until the ball contacts the ring or backboard."
"Cross" seems to imply breaking the plane. "...into the semicircle" seems to imply touching on the other side of the FT line.

Nowhere does it say what the penalty is. I guess because the POE cites 9-1-3g, we are to assume this is a violation. I wish they'd just have written a well-worded rule, then told us to insert it as 9-1-3h. How difficult would that have been?

After reviewing about 24 games from last season, this is significant.

BTW, this is almost exclusively a girls' thing. Boys games I studied didn't cross the FT line into the semi-circle. And it's typically the same girl the entire game--that over-eager player out to impress her coach with her aggressively paced entry into the lane across the FT line to box out the shooter. Is was what should be called a foul only three times times in those two dozen games. More often than not it's really borderline, which might merit a preventative mention early in the game, perhaps.
This might well turn out to be one of those "talk 'em out of it the first time you see it" or "get it early if it does happen and it won't happen again" things, it appears to me. At least based on the two dozen or so games and hundreds of free throws I analyzed.