[JRutledge]

I am not understanding the confusion here. When you straddle the division line, by rule you are located in the BC. If you touch a ball that has yet to reach BC status, then you have violated the backcourt rule. If the all touched the BC and then you touch the ball while straddling the line, then you are still in the BC and the ball had maintained BC status. The OP never said what happened to the ball clearly after the deflection.

So if the ball had FC status and then touched by a player located in the BC, the violation is because the player caused the ball to be in the BC.

Peace