There are places, you have to understand, where the dimensions-I'm not talking about that parallel dimension metaphysical stuff, I mean dimensions like length and breadth and time-where they curl into themselves, and begin to fester. Where foul things evolve and spread...
In a city where the justice system features judicial dueling, plaintiffs and defendants are permitted to request a champion to take their place in the duel: Someone chosen by lot from among the foreigners in the city. When anyone first arrives, they are given an enchanted ceramic pendant that marks them as a candidate for "court duty".
Wealthy folk entering the city are often escorted by burly guards, paid to carry pendants on their behalf: They elude court duty in that way.
Adventurers may seek work as a rich man's proxy or may find themselves magically summoned to serve as a champion.