I'm getting to the point where I need to do the conversion list, and after reviewing the thread, I've identified the following concepts:

1. The mechanic should be simple.
2. The effect should be consistent with the fluff.
3. The mechanic should be designed in such a way that astute players can compensate for it.

My first concept means that randomness and tables are right out. The minute you have to look up something, you are no longer simple.

The second one eliminates the whole "charge your own side result" as it is purely nonsensical. Orcs are itching to get into a scrape, not simply rabid and willing to fight anything within range.

The third concept means that players who use the appropriate "orc-y" style will benefit from it.

Thus my new rule is simply this:

At the start of the Orc movement phase, orc infantry units must either charge or run towards the enemy. Units that wish to move normally or remain stationary must make a command check to do so. If they fail, they fall into squabbling and lose their turn.

Black orcs are exempt, as is the unit led by the army commander. So are goblins, who aren't noted for their eagerness to engage in close combat.

That's pretty simple - if your army surges forward (the way orcs should), you never even notice the rule.

It's consistent with the fluff. The orcs' basic battle plan is "get 'em!"

It is easy for players to neutralize - simply set up your forces knowing you're going to either be swarming in or have a plan to hold the boys back. It does render orc archers kind of silly, but given the wider base size, they were never that useful anyway. Goblins shot just as well (with slightly shorter range) and were much cheaper.