How does Unferth affect Grendel?

Grendel encounters Unferth, a mighty warrior who would make a futile attempt to become Grendel’s nemesis. Grendel mocks Unferth’s heroic challenge by pelting him with apples, and then escapes back to his subterranean home. Unferth follows, swimming through the pool of fire-snakes to arrive, bedraggled and weak, in Grendel’s lair. Grendel mocks him further and, in an ultimate act of mockery, refuses to fight Unferth. Having failed to properly fight Grendel (or to be killed in the process), Unferth collapses from exhaustion. Grendel carries his limp body back to Hrothgar’s mead hall and deposits him there, much to the Danes’ astonishment and Unferth’s chagrin. From that point on, Unferth would occasionally attack Grendel on one of the monster’s raids, but to no avail.