The play described below is provided for your review and discussion. The rulings given are based on NFHS rules. NCAA rulings may be different.
B-1 scores with five seconds left to pull Team B within two points of Team A. After a timeout, A-1 throws a long pass from the end line which is caught by A-3 while A-3 is touching the sideline in frontcourt.
Handle the situation.
This is an out-of-bounds violation not a throw-in violation. Since this is an out-of-bounds violation, the ensuing throw-in will be from the spot where A-3 was touching the sideline not on the end line where A-1 was.
(References: Rule 9-2-2, 7-2-2)
Have you seen an unusual play? Let all officials benefit from it by sending it to Play of the Day

Correct. This play has to be administered correctly, or you give Team B a huge advantage.
Thanks!