(a) causes the ball to carom from the wall behind him/her, or from the floor out of bounds and then into the court;
(b) caroms the ball from the back of the backboard to a player in the court; or
(c) throws the ball against the side or the front face of the backboard, after which it rebounds into the hands of A2.
(b), since the throw touched an object out of bounds. The throw-in in
(c) is legal. The side and front face of the backboard are inbounds and, in this specific situation, are treated the same as the floor inbounds.