A possibility could be the rolled-up hockey nets for the 3x3x60 box, but I feel like they are much larger than that (and I am barely five feet tall).
My bet is that it's a field obstacle or field element of some sort that is necessary to be regulated amongst all teams. I'm pretty sure FIRST is backing down from having no field obstacles after seeing the damage caused in last years game.
Perhaps... It's something you throw Moon Rocks in?
