Interference?
 

R1 on first, attempting steal. Batter attempts bunt on a pitch over the plate. Batter misses bunt, catcher comes up stepping on the plate, where the batter left her bat. Catcher steps into the bat, effecting her throw. Interference?

Discarded equipment which is properly in the game is part of the field, regardless of where.

I think you misunderstood my question. The batter did not drop the bat, she just held it over the plate when the catcher made contact with it.

Yes, "plate, where the batter left her bat" fooled me.

If the position and movement of the bat is part of the attempt, then not interference.
If the bat was there because of a movement after the attempt which caused the hindrance (affecting her throw), then yes, interference.