All the following information needs verifying for accuracy on Horizon.
Will only activate if a hit is taken (even from 0 damage) from the front with your weapon drawn.
All defensive job abilities and skills (except potentially Shield) must be exhausted before Retaliation will take effect, and Retaliation will not negate or otherwise affect damage taken.
Unlike Counter, you gain TP from both the Retaliation swing and the damage you take to trigger the swing.