I wasnt talking about 5eThe direction a target faces is never mentionned in the rules. It's not a state represented by the game mechanics. Thus, there are no facing rules in DnD 5e.
When you said there were no facing rules you specified "in dnd". I was responding on the basis of all dnd. Back stab is an example. Attacking in general can be an example in some ways according to being concealed which you get an advantage toward if the npc is facing away. And other examples.