The question was more about the definition of "visual field." Again, I see it as a little bigger than a semicircle, from the left side to the right side of one's field of vision, as the neck is turned. I wanted to know if others see it that way. (No pun intended.)

Not always, but usually. This kid was taken out pretty hard, and I kept an eye on him as the play developed, but a shot was taken pretty quickly, and as soon as his team got the rebound, I whistled.

I Use My Protractor ...
 

Just the semicircle. Limited to 180 degrees. When the neck is turned, the semicircle is turned.

Hmmm, so let's say A-1 is running forward while looking over his left shoulder behind him. B-2 has LGP, and is directly in front of A-1. Since A-1's neck and semicircle are turned, would be B-2 be out of the field of vision, or is the semicircle based upon a player facing forward?

What difference does it make?

In determining the legality of the screen, "field of vision" applies only to a stationary opponent.

"Field of vision" does come into play in determing whether the player being screend commits a foul.

Gotcha, so this isn't even applicable to the formula I was developing. Thanks.

This is what I was getting at earlier; it only matters in determining how much contact you allow before you call a foul on the screened player.

Bob, somehow that statement doesn't sound right to me. As I mentioned earlier, I felt the "field of vision" doesn't determine the legality of the screen in that a player can legally set a screen within or outside the field of vision of an opponent. Rather, it is distance that determines the legality of the screen (should contact occur) on a screen set outside the visual field of the stationary defender. Would that be correct?

It's correct in the context of the post to which I was replying. "Field of vision" comes into play only when screening a stationary opponent; it is not a consideration when setting a screen on a moving opponent.

"Comes into play." That's the wording I was thinking of and also clears up (for me) why I was questioning your statement. Thank you (and to so many others on this forum) that give us knowledgable and consistently accurate answers. It has really been of help to me.