When you are wielding a finesse weapon with which you are proficient and another creature hits you with a melee attack, you can use your reaction to add 6 to your AC for that attack.
Defensive Duelist: 1 Reaction
When you are wielding a finesse weapon with which you are proficient and another creature hits you with a melee attack, you can use your reaction to add 6 to your AC for that attack.