[dahoopref]

I know you requested a NFHS ruling but here is the Men's NCAA ruling, scenario #3 was similar to the OP's play:

A.R. 215

The ball is at the disposal of Team A for a throw-in. A1 attempts
to throw the inbounds pass to A2, who is located in his frontcourt near the
division line.

3. A1’s throw-in pass is deflected by A2, who fumbles it into the
backcourt. A2 then goes into the backcourt and recovers the fumble.

RULING 3: Legal. This is not a back-court violation since neither player nor
team control had been established in the frontcourt.
(Rule 9-12.4, and 9-12.1 through .3, .5 through .7 and .9 through
.10)