Can A1 step on the OOB line when throwing the ball in as long as he/she doesn't step across it? I have heard both ways but can't seem to find any reference to it in the NFHS rule book/casebook.

See 7.1.1
 

Huskerblue,
The rule shows that a player on the line is out of bounds.
mick

The actual line they cannot cross is the edge of the line near the court. As long as no part of the shoe crosses that theoretical line, then the throw in is legal.

See NF rule 4-9 Boundary lines:

The inside edges of these lines define the inbounds and out-of-bounds areas.

Also see Rule 1-2:

The sidelines and end lines shall be a minimum of 2 inches in width.



Notice that it says "minimum." The lines can be 10", 20" or even more in thickness. Given that the location of the outside edge is variable from gym to gym, it follows that that edge does not mean anything. You would not require the thrower to stay 5' OOB (for a 5' thick line) on the throwin in only some gyms.

A thrower, as others have said, is OOB as required if they are not touching inbounds and are either touching OOB or in the air last having last touched OOB.

(Side note: if they jump on a designated spot throw-in, at least one foot must remain in the space over the spot: bounded by the OOB line on the front, the wall/bleachers on the back, and is 3 feet wide).

easy way to remember
 

If a player who is inbounds in player control steps on the line, he is OOB. Therefore, a player who is supposed to be OOB while inbounding can step on the line because it is OOB.

You can use this illustration to explain it to the stereotypical brilliant coach.

Those are really thick!
 

Camron,
I have never seen lines that thick: but, when I played football ,I used to trip over those thick yardage lines.:)
mick

Thank you folks.