When Gregor Clegane raids the Riverlands – well, he's not waving a flag, but we all know it's him – Eddard sends out a group of knights and warriors under the king's own banner (44 Eddard 11). This means that those knights aren't fighting for themselves or for their noble houses, but for the king. By which we mean, for peace and justice. Of course, this being a George R.R. Martin book, things don't work out for them. So much for justice.
This group consists of several nobles, such as Ser Gladden Wylde, Lothar Mallery, and Raymun Darry (who gets killed in the first ambush). There are also a whole bunch of non-nobles, including even some people we know about, like Alyn and Harwin, Stark family guards.
"Come for the tournament, stay for the conspiracy." That's what the tourism bureau of King's Landing should say. That's pretty much what Dondarrion does: he's an out-of-towner who comes for the Hand's tournament and decides to stick around. And while at court, he gets caught up in the game of thrones (where you either win or… well, you know). Though his party is pretty much destroyed by an ambush, Dondarrion continues to raid the Lannister army. That's why he's our twenty-one-year-old of the week. (How's that for a reality check?)
Our other favorite member of the Dondarrion party is Thoros of Myr, a fat foreigner (Myr is one of the Free Cities), who shaves his head and somehow still looks cool with his sword on fire. (Do not try this at home.) That's his secret for winning tournament melees and real battles (31 Eddard 7.93). Thoros is kind of a weird-seeming guy (30 Sansa 2.2), but he is a useful reminder that the world is bigger than just this war in Westeros: not only is Thoros from Myr, but he's also a Red Priest, a follower of a religion that we don't see much of in the Seven Kingdoms.