spot throw in

[Altor]

I don't see a difference between 1) asking the player making the throw-in to back up a bit when his/her toes extend over the boundary line, 2) asking the defender to back up a bit if they are already encroaching the boundary, or 3) telling the offense that only one player may be OOB during a spot throw-in
before you administer the ball for a throw-in.

If you wouldn't ask the player if they were ready when their toes are over the line without pointing out the reason for your question, why would you do it in the OP?