Think of it this way: you narrate the beginning of the NPC's action, but stop before the outcome is decided: "The ogre is swinging his club down at you." That's your threatening move. Then the player reacts: they can jump out of the way and Defy Danger, they can parry and attack with Hack & Slash. The player's roll decides the outcome of your NPC's action.

Sometimes the player has ignored a threat, or been forced to choose between two threats, like an archer is shooting at them simultaneously but they choose to Hack & Slash the ogre anyway. In that case, their roll determines the ogre's outcome but you might say that they take an arrow because they didn't try to hide or dodge.

Does that help? It helped me to think of it that way. Playing the game is very natural in practice, it's not as awkward as it might sound.