Possesion

[FishinRef]

There are several exceptions to the "Backcourt Violation".
Look in Case Book at 9.9.1.B.
It describes a jump ball sitch, but the same procedure exists on a throw-in. The key is that the player is AIRBORN when they receive the ball and establish Team Control.
9.9.1.A describes the player having "One Foot" in A's frontcourt when Team Control is established.
IMO the best way to think of it is, where is the player & ball when the ball is PUT IN PLAY. We all know it is a LIVE BALL when at the disposal of the thrower.