To answer your definition literally:
"According to Aristotle, a Greek tragedy includes an:
1. Incentive moment: pre-existing "in medias res" situation that achieves unity of time, place)
2. Peripeteia/Rising Action: a series of rising actions induced by the tragic hero that inevitably bring about his downfall rather than prevent it, which is his intention
3. Anagnorisis/Climax: a turn of events that leads to the tragic hero's inevitable suffering, but he is not as aware of it as we, the audience, is.
4. Catastrophe/Falling Action: the tragic hero becomes aware of the fact that he has caused his own fall, and he punishes himself or expresses guilt, shame, or responsibility.
5. Resolution: the Chorus usually adds a moral exemplum after the tragic hero leaves the stage.
* And it must conform to the three unities: unity of time (take place during one day), unity of place (one setting), and unity of action (begin at the end with no flashbacks).
* It must focus first on plot (the 5 parts of the Aristotle triangle) and character, focusing on the tragic hero who suffers from a tragic flaw (hamartia), usually pride. My favorite definition of tragic hero comes from critic Northrop Frye:
“Tragic heroes are so much the highest points in their human landscape that they seem the inevitable conductors of the power about them, great trees more likely to be struck by lightning than a clump of grass. Conductors may of course be instruments as well as victims of the divine lightning.”
So, the gods send down tragedy in the form of lightning. The tragic hero Creon is the "highest point" in the human landscape since he is king, and he becomes a conductor of tragic lightning to others, the "clump(s) of grass" (Antigone, Haemon, Eruydice). It is Creon's decision not to bury his nephew is the sacriligeous inciting incident that leads to the gods' punishment of him. Antigone may be a tragic hero, but I think of her more as an agent of the gods: a kind of lightning bolt herself.