where do you mark the penalty?

[GeorgiaBlue]

I see no need to use a beanbag on a backwards pass - it was simply intercepted, not fumbled.

A fumble is any loss of player possession other than by handing, PASSING, or legal kick.

So there would be no beanbag on the turnover.

2-18 for fumble.
2-22 for interception.

For those that beanbag backward passes - you are doing so unnecessarily.