Just came across this on the NFHS site.
SITUATION 5: A1 has the ball for an end-line throw-in in his/her frontcourt. A1’s pass to A2, who is in the frontcourt standing near the division line, is high and deflects off A2’s hand and goes into Team A’s backcourt. A2 is then the first to control the ball in Team A’s backcourt.
RULING: Legal. There is no backcourt violation since player and team control had not yet been established in Team A’s frontcourt before the ball went into Team A’s backcourt. The throw-in ends when A2 legally touches the ball, but the backcourt count does not start until A2 gains control in his/her backcourt. (4-12-2d; 9-9)
Here's the whole document:
NFHS | 2011-12 NFHS Basketball Rules Interpretations