This part of the book the rising action, showing the reader that Beowulf is strong and heroic with no signs of fear. It is also like a pre-climax because this is one of his biggest achievments in the whole story.
This part of the story would be more of the main climax because Beowulf has taken down beasts that no man ever could. When he's crowned, it's after he has shown great valor and loyalty to his former king.
This is the falling action/resolution because Beowulf fights his last battle at such an old age, even when the odds are against him. In the end, he slays the beast and dies in the process, leaving his people very sad but proud of his heroism.