A peritrope is a turning of the tables
, most usually in a debate
to win some advantage
For example, in Plato's Theaetetus Section 171a, it is used against Protagoras to reject his relativism. Protagoras says that whatever seems true for a person is true for them. So, says Plato, through the character of Socrates, he must then accept that those who believe that the doctrine of Protagoras is false are right, because obviously its falsity must be true for them. At his point Protagoras flounders for a bit, and then comes up with something else to talk about. Plato uses this kind of thing a lot.
A nice little rhetorical trick, it was gainfully employed in recorded texts by Epictetus (Enchiridion) as well as others since.