A band of Deserters.
Deserters are a special kind of bandits. The biggest difference between them and usual brigand is that deserters are far more organized and strategic, with much better equipment. This is because their gangs mainly consist of regular units, sometimes appearing in big, high-tier unit groups.
Deserters are soldiers who left their kingdom to live as "free brothers". The player can encounter them anywhere, but are more common in border regions where conflicts have occurred. They usually come in medium sized parties of a single troop type, e.g. 20 Swadian Militia. They are often more hostile than similarly sized parties of Looters and will usually drop much better equipment than other neutral hostile parties.
If they encounter the player, they will demand a relatively small amount of money (at least to somewhat experienced players), and if not paid, they will attack.