As a villager myself, at one point, I waited for a fight to end, in my opinion, and then jumped and killed the mage. I learned from the Drillmaster and Kastellyn himself that if you are waiting for your turn to beat on someone while they are beat down, you are not holding up to the spirit of the one on one fight. You are basically spitting in the face of that spirit. Now, if you had no idea that the fight was going on and you happen to have just ran into an enemy, that isn't your fault.