[Nevadaref]

It is a violation. There is TEAM control during the entire play. What confused you is that A2 never had PLAYER control. However, that is not a requirement for a backcourt violation.

If the ball was first deflected by B1 and then went off A2's hands, it would still be a violation. The important thing to remember is which team is the last to touch the ball before it goes into the backcourt.

Therefore, the reverse would not be a violation. (Off A2's hands then deflected away and into the backcourt by B1.)

PS There is a case book play for your situation:
9.9.1 SITUATION C: A1 is dribbling in his/her backcourt and throws a pass to the frontcourt. While standing in A's frontcourt: (a) A2 or (b) B3 touches the ball and deflects it back to A's backcourt. A2 recovers in the backcourt. RULING: In (a), it is a violation. The ball was in control of Team A, and a player from A was the last to touch the ball in frontcourt and a player of A was the first to touch it after it returned to the back court. In (b), legal play. A Team A player was not the last to touch the ball in the frontcourt. Team A is entitled to a new 10-second count.