When Anthony claims he is not a good orator, it is an example of what

Antony uses sarcasm in his rhetoric by hiding behind humility.

Explanation:

Antony starts his speech by saying that he is not a good orator but lays out one of the most eloquent speeches that by its own virtue turns the people against the assailants whom they were supporting till then.

What Antony did here was multifaceted

This made the audience fall for the rhetoric of his speech that was his goal.

his face was as red as an