What is Beowulf's behavior before and during his battle with Grendel?
Beowulf's behavior is that of a typical hero in the epic tradition. First, we have Beowulf sailing to the aid of Hrothgar to reciprocate for Hrothgar's helping his father. This shows Beowulf to be of noble and responsible character, loyal to his family and embedded within a reciprocal network of social and military obligations. Beowulf engages in a battle of words with Unferth, and in his description of the swimming contest and vanquishing of the sea monster does two things, foreshadows his victory over Grendel (who is also a monster associated with the sea) and begins a classic pattern of the boasting in which heroes of oral epics typically indulge before a major battle.
At the start of the battle, Beowulf remembers his boasts and uses them to grant him to courage to fight Grendel. Because no weapon can wound Grendel, Beowulf rips off the monster's arm, and afterwards it is displayed as a trophy. Beowulf then attends a banquet and is richly rewarded by Hrothgar.