Beowulf is an Anglo-Saxon epic which features the hero, Beowulf, as he comes to save Hrothgar and his people from the marauder known as Grendel.
We only have a few clues about why Grendel is so outraged by Hrothgar and the typical Anglo-Saxon revelries which happen at his mead-hall, Heorot. None of them are enough to justify Grendel's twelve years of murderous marauding, however, and all of Hrothgar's people are thrilled that Beowulf has come to save them by killing Grendel.
Beowulf boasts that he will lie in wait for the monster and then fight him without weapons, just as Grendel does his killing; and that is what he does. Grendel arrives at Heorot, not knowing what is ahead for him.
Higelac’s hardy henchman and kinsman
Held him by the hand; hateful to other
Grendel is sorely wounded.
Was each one if living. A body-wound suffered
The direful demon, damage incurable
His body bursts.
Was seen on his shoulder, his sinews were shivered,
His body did burst. To Beowulf was given
Glory in battle; Grendel from thenceward
Must flee and hide him in the fen-cliffs and marshes,
Sick unto death, his dwelling must look for
Unwinsome and woful; he wist the more fully
The monster flees away to hide in the moors.
The end of his earthly existence was nearing,
His life-days’ limits.
Beowulf, who was said to have the strength of twenty men in one arm, fights Grendel, who is able to carry away thirty strong men at a time. They do battle arm-to-arm, and Beowulf wins. Grendel's entire arm is pulled out of its socket, and the monster "flees away to hide in the moors" where he soon dies.