Would having some surface or object as part of the robot that is slowing and possibly stopping balls that hit it count as possession? For example, if there was a net that balls passed through where those balls then sat under the robot, but were not in contact with the robot afterwards?
Additionally, would balls placed on top of the robot count as possession, if those balls are not being actively moved by the robot they are placed on while the robot has 4 balls already in possession?
And lastly, would a convex ramp/bumb that directs balls towards the robot (and is attached to that robot) count as possession? This would be something like the horizontal cross-section of a torus.