If your electronics are inside the robot, then you are ok. You could just put bar over it to prevent balls from falling inside. However, if the electronics are vertical and facing outwards where other robots may hit it, then it must be covered. Tell your team members this one more time and end it with, "If you don't, then we're sooooo screwed at competition and I will enjoy saying 'I told you so', over and over."
But seriously, COVER IT!