I just had a battle in-game where a Riolu used feint, and it hit, despite me having used neither protect or detect. As far as I'm aware, the move should miss unless either of those moves are used prior to it?
If it helps, the trainer was "Hiker Jerome" on Route 20, the guy who stands at the top of the stairs and stops you moving forwards until you're found the Herdier and beaten the first gym.
If you don't know, the effect of Feint was changed in gen 5. It hits the foe first no matter if it has used Protect or Detect