The largely fictional practice recorded in medieval romances of a knight setting up camp at a bridge, ford or other choke point and challenging all comers - or at least all armigerous comers - to combat. He may be trying to perfect his skill by fighting against as many opponents as possible or playing king-of-the-hill in search of a knight skilled enough to defeat him. In slightly more realistic settings he may be after money instead.
This was generally the province of a knight errant and the challenge was likely to be for a few friendly passes of arms to determine who was most skillfull. Sometimes the disputing knight and someone that he has challenged will become friends - in some versions of the Arthurian Cycle Lancelot meets Arthur whilst disputing a bridge - Robin Hood and Little John meet in much the same way in many versions, offering a more proletarian equivalent of the trope.
Of course if the disputing knight is a black knight in the villainous tradition - or even if both parties are merely fiercely competitive - the challenge could be a lot more violent. Betting may or may not be involved in all cases, as may or may not ransom and forfeiture of the defeated party.
Traditionally the disputing knight doesn't hold the ford against non-combattants or commercial traffic (that would make him some kind of dishonourable robber knight) - although a sufficiently base villainous black knight might do so - or allow his retinue to. It would also be entirely genre-appropriate for a less honourable disputant to kidnap a passing damsel for various reasons - marriage, ransom or to annoy her family or betrothed would seem appropriate.
Whilst this may have occured in real life - probably during the tournament season when there were large numbers of compulsive jousters rattling about between the various formal competitions - the next nearest equivalent would probably be a knight set in command of his lord's toll gate who has become bored out in the middle of nowhere and started challenging people for fun.
A similar action known as a pas d'armes in which a group of knights disputed some terrain feature occured occasionally - from time to time escalating to the level of a mini-tournament - although just how often this actually took place, and how much was the recycling of the romances as fact is unclear.
Since this is largely fictional, a GM or writer could easily expand the idea of disputation to other professions - scholars or theologians who challenge any passing peer to a debate1, magicians looking for a friendly form of certamen or just someone to compare thaumaturgical notes with. Bards might offer a rhyming contest and other combattant professions might offer other kinds of martial contest.
The challenge offered might even be a game of chess or something… whatever it is it should be a contest of equals - very few knights will compete seriously against a raw squire (but they might deal very roughly with a "jumped up commoner" under arms … or at least try to do so), nor would they joust a non-armiger. Likewise a philosopher is unlikely to trouble himself with debating a passing warrior - unless the traveller happens to be a man of many parts. Only an obvious opponent is likely to receive a direct challenge, although a character's ego may demand that he challenge a disputer who doesn't challenge him…
To be absolutely true to form the challenge should be declinable (if the challenged party can accept the loss of face) and serious enough that the PCs can benefit experience wise from the exchange. This is also a good way to introduce new NPCs (or PCs even) - including arc rivals, tutors and people they will need to track down later for help or information.
A tale of disputation from the Charlemagne Romances
Wikipedia on the Pas d'Armes - the real life equivalent
Game and Story Use
- This doesn't fit all that well in a setting where personal reputation doesn't count for much, so modern campaigns should probably avoid it, but it should fit nicely into a martial arts campaign (replacing the knight with a brash younger rising master) or even a western - if the disputer is a boxer or wrestler.
- The local champion prizefighter challenging a visitor who is a known bruiser himself, or even the carny fighter who's manager offers a prize to any local who can stand a given number of rounds with him might count as well.
- On that theme, a lot of rougher neighbourhoods have a boxing club, or other sports club, where defeating the local champion - or at least putting on a credible performance - might give the PCs the opening they need for an investigation.
- Does Stiffler's dance-off in American Wedding count or is that more Scry vs. Scry?