Order of the Knight of The Shield
This is one of the Orders of The Shield, and is in fact the oldest and most numerous.
Long ago the Knights of the Shield were a popular group of knights who upheld the ideals of honor, good, and gentility. Being a land that had no nobility, anyone who joined the Knights were considered one. As their success grew, they absorbed other military forces, until they were all that was left on their island. With no local enemy they looked to organizing the land, making them the first organized government and start of a new country.
As groups with similar interests started to join together, the government laid the system which led to the Orders of The Shield. The Knights of the Shield were made into the Order of the Knight of The Shield, which at the time was basically the army.
Now their role is largely unchanged. The Order of the Knight of The Shield is still the main army of The Shield. They are also the most numerous, not only because a soldier is a straightforward job, but because this is the Order with the most glorious history.
While they are expected to act as a member of The Shield just as much as anyone else, it is inevitable that a group of this size has some people who are “just soldiers”, or even “just here to fight”. Obviously this is one of the most common Orders of The Shield a person would encounter, including the most likely origins of a questing Crusader.