A coalition of Squires and Knights of the Lion defeat the Sarleon Deserters.
There are several types of "deserter" units, one for each of the major kingdoms. The only unit in which a player will see large numbers of deserters is the Peasant Revolt Army, although specifically Sarleon Deserters can be seen in two other major spawns.
Sarleon Deserters are the core infantry aspect of Alaric von Brouhaha if the revolt is in the Sarleon region. They are equipped with medium armor such as 'Surcoat over mail' and 'brown padded leather'. They also use swords, kite shields, spears, and awlpikes. Most Sarleon Deserters do not don helmets. They generally pose no threat to an army of well armed cavalry, but can cause significant damage towards lower tier units. Sarleon Deserters are also part of the army of The Three Seers.
The other Deserters - Empire, Fierdsvain, D'Shar, and Ravenstern - are likewise poorly equipped. Empire Deserters tend to favor polearms and shields, while Fierdsvain Deserters often receive two-handed axes. Ravenstern Deserters are the poorest equipped. When engaging the Peasant Revolt Army, if your party is composed of solid forces, you should win easily; however when on horseback you should still watch out for the polearms of the Sarleon and Empire Deserters in particular, as they can stop your mount cold and allow the peasants to swarm you.
D'Shar Deserters are rarely seen, only appearing for certain in the hireable mercenary company Lothario's Brotherhood.