Throw In Rule Question
 

I don't have the rulebook in front of me but I seem to think that the rule regarding a spot throw in does not limit the depth but does limit the width on a throw in. However, it also says something about keeping one foot on or over the throw-in spot. I may be missing key wording.

When it says "on or over the throw in spot" is that only limiting it to the width?

Ex: A particular floor has 10 feet from the endline to the back wall. A1 stands about 6 to 8 feet off the line and the official hands her/him the ball. A1 then runs forward all the way to the end line and throws a long pass. Is she still "on or over the throw in spot assuming she didn't go outside the width limitation?

Yep, you have the correct understanding.

Here's the rule reference:
4-42-6 . . . The designated throw-in spot is 3 feet wide with no depth limitation
and is established by the official prior to putting the ball at the thrower’s disposal.
NOTE: The thrower must keep one foot on or over the spot until the ball is released.
Pivot-foot restrictions and the traveling rule are not in effect for a throw-in.

Substantial penalty for early withdrawal.
 

A player inbounding the ball may step on, but not over the line. During a designated spot throwin, the player inbounding the ball must keep one foot on or over the three-foot wide designated spot. An inbounding player is allowed to jump or move one or both feet. A player inbounding the ball may move backward as far as the five-second time limit or space allows. If player moves outside the three-foot wide designated spot it is a violation, not travelling.

How is the 3' measured? I mean is the center of the 3' where the player is standing when handed the ball or is it up to the official?

The same way I count to 21. ;)

So the OP got me thinking: If that scenario takes place (running forward, toward the endline), the inbounder can jump but better not break the plane -- with both feet, as it were -- before releasing the ball, correct? Because the inbounder can reach the ball through the plane to inbound BUT also must keep one foot on or over the 3-foot-wide spot. Right? (Never seen it happen but ...)

4.42.6
 

ART. 6 . . . The designated throw-in spot is 3 feet wide with no depth limitation and is established by the official prior to putting the ball at the thrower's disposal.
NOTE: The thrower must keep one foot on or over the spot until the ball is released. Pivot-foot restrictions and the traveling rule are not in effect for a throw-in.

Yes, and we've discussed that scenario before.