I'm using shield on duel for the same reason...
No Harpag, w/e you tell yourself, you use a shield because you are truly fucking awful at this game. Im sure you are great at organising nice lists of cd-keys, asperging like mad over the strat map, but playing warband is not your strong suit. Infact its not even in your pack.
EDIT:
Mocking Noobag made me forget my point I was going to make in this thread
Shields are not for fighting with. They just are not. They slow you down, they are not reliable when it comes to block coverage, they just are not for fighting. If you use a shield in a 1v1 fight you are gimping yourself.
Shields are for putting between your pretty face and bundle of stickss cumming streams of arrows and bolts at you, that is their purpose. But: 1h is the least viable option for 1v1. Both polearms and 2h have longer, faster, more damaging weapons. Currently the most broken things ingame are curved 2handers and w/e the fuck that idiot Tydeus has done to polearm animations/speed. But if you ARE going to use a 1hander, always take shield skill, being able to run straight for ranged fucks is priceless. But you also gotta make sure you rebind "Drop shield" to something convenient.
Anyone with anything even vaguely axe shaped comes my way I drop my shield, because I value it too much to use in melee.
As for dueling: if people are giving you shit about what you are using, press ESC, player list, muted, done, happydays.