After still further review...

I spent much of my break making upgrades to some of my armies - finishing some units, refinishing others. The orcs were one I worked on. Chaos was the other.

Both Orcs and Beastmen have variations on Animosity (Beastmen call it Infighting). I was also reminded that there's a Stupidity rule, which ties into leadership.

All three of these rules are based on the simple premise that some troops simply don't do what they are told. This lack of discipline is distinct from low morale or fighting spirit, however. Once in a fight, they all do reasonably well, they just have a problem following orders.

Thus I'm going to create a single rule (whose name I haven't settled on yet - Feral, Insubordinate and Rebellious are candidates) that kicks in if the player rolls a 1 on a d6 at the start of a turn when they aren't in combat.

Depending on the army, the next step will vary. They may just stand there, or they may attack their own side, and these rolls might be modified. The idea is to create a single special rule that impacts different armies in different (and characterful) ways.

The other idea is to make the rule optional and to give a discount for applying it. This is because command and control can vary considerably, particularly in evil (but also non-evil) armies.

For example, orcs led by one of their own (a low-rent thug) might have units that balk at obeying orders, while those led by a Dark Lord of power (the Witch-King of Angmar) wouldn't dare disobey. This gives players flexibility on how they structure their forces to fit the theme of their engagement.

Are your orcs/beastmen/etc. a collectly of motley tribes united only by a thirst for loot and plunder chose chiefs are constantly jockeying for position or are they dull, drilled, docile masses of brutish soldiery who fear their commander more than the enemy?

This allows for both.