Let me tell you a bit about the medieval Ynfidion.
The native accounts and chronicles contain accounts of these groups of violent and impetuous youths who would roam Wales causing not only mischief but often political upheaval.
These ynfidion, "hotheads, fools" sat in a space between bandits and rebels, youths raised in a martial society which glorified violence and military prowess, eager for excitement, wealth and glory who would attach themselves to those who they felt were best placed to provide
This often came in the form of an exiled or dispossessed prince whom they could coalesce around and who's political aspirations would provide them the honour, violence and loot they sought.
The followings of Gruffudd ap Rhys and Owain ap Cadwgan were described as "ynfidion"
These two men were two of the most prominent "landless" princes of medieval Wales. Gruffudd a man who's patrimony had been overrun by the Normans and who was forced to take to the woods to wage a conflict for his restoration.
Owain, a famously tempestuous member of the Royal house of Powys who's life reads like a cross between violent outlaw and daring adventurer.
These kinds of men, as they did in other societies, inevitably attracted the support of the bored, the disaffected and the violent.
This in essence was a personal warband. United not by the ties of service, loyalty, homage and duty which characterised the teulu (household guard) or a host raised by a legally empowered ruler, rather it was a "gang" united by personal interest and a desire for glory.
And this it has been argued is at the core of the judgemental name 'ynfidion'. Being men who rejected the traditional vertical structure of society based on service and loyalty between a Lord and his dependents, and instead serving a man outside of their traditional hierarchy
It's a gang basically. A big violent gang led by a man with political aspirations and the right kind of lineage and name to attract men to his cause who fight for him and support those aspirations because they trust he will provide them with wealth, power, glory and adventure