"Defeat tribues" is an objective in the quest The Hunger Pangs in The Horrible Hunger of the Ravenous Wattle Gobbler DLC
Head to the final piece of Skag Meat. As you approach it, President Smith will send the first pair of tributes at you: William, Tribute of Wurmwater and Glasspool, Tribute of Wurmwater. Defeat them and you will be able to get at the final piece of skag meat.
To reach the final piece of Skag Meat head over to the East. Head into the room there and go through to the second one. Take the stairs in that one up to reach platform that will take you straight out to the final piece of meat.