Grendel approaches Heorot and tears open the doors. He grabs a sleeping Geat, Hondscioh, and eats him quickly. Grendel next reaches for Beowulf but Beowulf grabs Grendel's arm with a grip stronger than any Grendel has felt before. Grendel becomes frightened, but Beowulf's hold is too strong for Grendel to escape.
Grendel, an outsider who spurns society, and Beowulf, an outsider who joins the Danes in fellowship, battle. Beowulf makes good on his boast that he will fight Grendel single-handed.
Grendel's fierce cries and the sounds of their epic struggle wake the warriors. Heorot shakes with the force of their fight. The men grab their weapons to help, not knowing that a spell protects Grendel from all swords.
Fate (or God) does reward Beowulf's courage: if he had used a sword rather than his bare hands he wouldn't have been able to harm Grendel.
Finally, Beowulf rips Grendel's arm and shoulder from its socket, and the monster, mortally wounded, flees to the swamp to die. Beowulf mounts Grendel's arm as a trophy on the wall of Heorot. Beowulf, the narrator says, has fulfilled his boasts.
Beowulf proves himself as a warrior by fulfilling his boast. Mounting Grendel's arm in Heorot, the heart of Danish society, symbolizes society's victory over the outcast.