What is Antigone's hamartia?

The first thing we have to ask when considering hamartia in Antigone is, whose hamartia are we discussing? Antigone's name is at the top of the program, but is she the tragic hero of her own play? Antigone doesn't fulfill the requirements of a traditional tragic hero.
A tragic hero suffers a significant downfall, usually from a high status to a low status. At the end of the play, Antigone is at the same political, economic, and societal status that she was at the beginning of the play, even after she takes her life.
A tragic hero undergoes a life-changing psychological, emotional, or physical transformation as the result of their tragic flaw and their decisions. Antigone undergoes no such transformation. Her psychological, emotional, and physical states don't change. The only transformation she undergoes is from life to death, which, quite frankly, isn't enough on its own for Antigone to be considered the tragic hero of the play.
Hamartia is not just the hero's tragic flaw; it encompasses the decisions the hero makes based on that tragic flaw and the effect that the decision has on the hero themselves and on other characters in the play.
Antigone is willful, stubborn, and single-minded in her beliefs, but these beliefs, and her decisions, are based on moral and ethical considerations and on what Antigone firmly believes is the will of the gods. These are Antigone's character or personality traits, not hubris, and these traits do not represent a tragic flaw.
This is the significant difference between Antigone and Creon. Antigone knows what she's doing by burying Polyneices: she knows the consequences, she does it on purpose, and it's no surprise or sudden realization to her when she's punished exactly as she expected. Antigone's decision to bury Polyneices is simply the catalyst for Creon's hamartia.
Creon is admonished by Tieresias, who says the gods are angry with him, the Theban people's prayers are going unanswered, the people are suffering from a plague, and neighboring city-states are threatening Thebes as a result of Creon's decree and his decision to punish Antigone. The decision he makes to punish Antigone in spite of everyone around him advising and arguing to the contrary is based solely on his own hubris, and this represents Creon's hamartia.
Creon doesn't know—and doesn't realize until it's far too late—that the effect of his decisions will be that Antigone, Haemon, and Eurydice (Creon's wife) will all kill themselves and that he will suffer the fall that all tragic heroes suffer.

CREON: . . . And on my head I feel the heavy weightOf crushing Fate.