As far as I’m aware SG6 is the only rule that could limit possession of opposing mobile goals.
What constitutes grasping, grappling, or attaching:
Can a robot push opposing mobile goals with a concave surface?
Can a robot pick up opposing mobile goals provided it does so without reacting against multiple sides (eg scooping it from the bottom)?
Can a robot carry opposing mobile goals on a flat or concave surface that is much larger than the mobile goals (that is the goals loosely lie in a bowl/plate on the robot)?