Another back court question

[BSL]

Fellow Officials,
A situation I had happen tonight while officiating a basketball game that I thought I would ask the opinion of the professionals. Team A had control of the ball in their front court. A1 threw the ball to A2, but it goes over his head and hits directly on the 10 second (half court) line. After it hits and bounces in the air A3 jumps from the front court, grabs the ball, turns while in the air and throws the ball back to A2 in their front court before he lands in the back court. I did not call this a back court violation. I struggled a little bit finding this exact rule in the rules books. Can anyone please help me.

Thank you,
Brian S. Laffoon