Just curious. We've done a few back flips in the gym occasionally. I was wondering, for a beginner, would not being able to do a split/very flexible prevent you from doing a back handspring?
Bingo. You don't need back flexibility at all for BHS. If you can hold a HS, you don't even need a bridge on ground really as just knowing the bridge shape with feet elevated would be enough.
It's nice to be able to back limber before BHS though.