I'm sure if I searched for this topic it's already been covered... but I'm taking this as an opportunity to plug this great game.
I played RRtK solo again last night for the first time in a while. Such great fun; the reaction system captures the chaos of a mass battle better than anything else I've tried.
Anyways, the Uruk (Later Sumerian) CinC's Chariot was routed, forcing the Leader Lost reaction check for the Uruk army. Several melee units passed 1d6 only, resulting in a "retire" result. These units were not in melee or even close to enemy units.
The question is: in which direction do these units retire? Away from the "source" of the reaction check (their routing Leader), or away from the nearest enemy, or away from all enemies? I chose the latter and had them move their retire distance in a composite direction that took them the farthest, on average, from all enemies. If I tried to move them away from the nearest enemy it would have pushed, at least one unit, closer to another enemy.