To be honest, much like the real thing, most of the tension is before the duel. Duels need a good set up I feel.
I agree with this. A duel without a cool in-game plot reason that builds up to it is kind of *meh* imho. The biggest problem I've had (as a player; I've never run a duel) is that the non-dueling PCs are left out-- even if they're off doing something else. And frankly, the couple I've witnessed (a mage duel and a courtly challenge) were simply boring-- though that probably had more to do with the chemistry of the DM & player in question.
Anyway, my thoughts on running a duel basically mirror most everyone else's:
** Ways enforce a duel between two rather than normal combat:
- a code or moral alignment (eg, a devil vs a paladin, each is lawful and each keeps his word)
- physical isolation (the duelists are alone on a pinnacle, in a cage-fight or arena, etc)
-supernatural reason (when the agreement is made, the duelists are whisked away to an arena guarded by inevitables; Something Bad (TM) will happen if anyone interferes, a prophecy is undone, an Artifact self-destructs, etc).
** Making it interesting to watch, for those not fighting:
- cool terrain (moving platforms, set pieces, hazards)
- unusual constraints (special weapons ["Bring out the lirpa!] or armor- or none, blindfolds, duelists chained together, etc)
- cultural considerations (special weaponry or armor "Bring out the lirpas!", sacred location, draw no blood/use no magic or risk offense)
** Involving other PCs, and/or keeping them from interfering:
- they're busy elsewhere (*meh*)
- they're keeping area clear for duelists (eg, in a greater battle, they're fighting at the fringe, preventing BBEG's minions from helping him)
- they're "judging", "witnessing" or otherwise honorbound (lest Something Bad (TM) happen to them).
- each one is caught in his own duel (eg, with their counterparts in a rival party (Elan vs Nale), aleaxes, etc)