It is important to keep in mind that the public areas of the game are always quite likely to be populated by various NPCs—courtiers, knights, guardsmen, servants, stablehands and so on in the castles and the general populace of the cities in other areas. If events out of the ordinary take place—events that would be disruptive to the normal day-to-day operation of the castles or cities—it’s entirely likely that some NPCs will get involved one way or another.
If there is significant violence, with weapons being drawn, the gold cloaks of King’s Landing and shariffs of Sunspear would interfere, even if those involved are nobles. Players should feel free to @emit such cases where violent or criminal action involving one or more parties get broken up by the City Watch. They’re there to keep the peace, and while they may hesitate when it’s their betters breaking it, they won’t hesitate forever.
Another important category of NPCs to keep in mind are the escorts that may accompany various characters, especially younger ones. Unmarried girls in King’s Landing are unlikely to be without a septa as a chaperone, for example. Players should be mindful of this when roleplaying behaviour that is, again, out of the norm and/or transgressive—NPCs, even those who might be in their train, are often not likely to agree with this behaviour and may even be in a position to tell them so.
Finally, when it comes to NPCs in general (rather than a specific NPC), it is important to be careful in regards to how their opinions are characterised in roleplay. How NPCs at large feel about an event or about a character should generally be determined by Staff.