This dataset provides details about each time we observed two banded mongoose groups engaging in what ended up being lethal conflict at our field site (Mweya, Uganda) between 2000-2011. The dataset provides information about which group won the contest (measured by which group ran from the location of the fight), which individual died in the battle, whether that individual was in the losing or winning group, and the date. The purpose of this data was to estimate the proportion of mortalities which come from winning groups vs. losing groups.