Ass whooping radius is an area around an individual who is getting their ass whooped. This radius can result in others who find themselves within it, to be subject to an ass whooping too. Just by standing / sitting in the area as a bystander or giving a funny look to the person who is administering the beating, can result in the bystander being beaten.
"Chris's mother is punishing him. You'll get your ass beaten too by her, just by sitting in the ass whooping radius!"