Hamarta, as detailed by Aristotle in Poetics, is defined as a fatal flaw, or more commonly a mistake.
Agamemnon showed hamartia in many things.
1. Agamemnon showed hamartia by walking on the tapestries which depicted images of the gods.
2. Agamemnon accepted honors which many deemed extravagant.
3. Agamemnon asks for men to show him reverence even though his declares himself to be a mortal man and not a god.
4. Even though he stands on the tapestries showing the images of the gods, Agamemnon declares that he should not be struck down by the wrath of the gods.
Overall, Agamemnon declares himself to be more powerful than that of the gods. His outright disdain for the power of the gods, and his claiming to be held up like a god, proved him to be filled with a fatal flaw, or hamartia.