Duel Mode is a special gametype in JK3 where two fighters from everyone on the server fight eachother while everyone else watches in spectator mode. The winner continues to fight and the loser goes to the bottom of the list of those waiting to fight. Both fighters start with 100 HP and the damagescale is adjusted to make hits do less damage - prolonging the fight. All fighters on the server can look at their scoreboard and see how many kills and deaths they have gotten. Dualmode usually has rounds either decided by one player reaching a certain number of kills or by a timelimit. In the event of a timelimit win, the fighter with the greatest amount of HP remaining wins. There are an entire group of duel maps that come standard with the game for players to enjoy this gametype on.
"g_gametype 3" enables the duel gametype
"fraglimit 1" makes it so a fighter only has to win 1 duel to advance to the next fighter