Deadliest Warrior Battlegrounds

When playing a private match against bots from the Custom Game Menu, make sure to set your map to "Fortress". Then the option for the game type "Dual Match" becomes available at the bottom. Once you start a game, simply melee one of the bot AIs and get into a duel. Play out the duel (until one of you dies). Repeat four more times for the achievement.

NOTE - you do not have to win any of the matches or the round.