The feat Warforged Superiority from Martial Power 2 reads like so:
Prerequisite: Warforged, fighter, Combat Superiority class feature
Benefit: Whenever you hit a creature with an opportunity attack granted by Combat Superiority, you also knock that creature prone.
But Combat Superiority, defined in the Player's Handbook, doesn't grant attacks. It gives you a bonus to opportunity attack rolls, and stops anybody you hit with one.
Combat Challenge, on the other hand, does grant attacks, but they're immediate interrupts not opportunity attacks.
Did they mean Combat Challenge, or is the 'granted by' phrasing a typo?
This feat seems like it would be a lot more helpful if they meant Combat Challenge. I haven't looked up all the relevant rules, but it seems like an immediate interrupt that knocks a creature prone would stop their movement, which already happens with Combat Superiority, but not with Combat Challenge.