I realize this question is probably answerable myself (in that I've read the minion rules). But I wanted to make sure I'm not missing something. Also, discuss the reasonableness of several possible answers/tactics.

Let's have two minion groups, say of 4 Imperial Stormtroopers each, find themselves in an off-duty situation wherein they get caught up in a barroom brawl with a group of PCs, a rowdy cantina full of patrons, and various other insundry ne'er-do-wells.

The crux of the issue lies with Brawl not being a group skill for Stormtroopers. So by the rules they do not benefit from upgrades while using said skill.

As a GM, what do you/have you/are you supposed to do in a case like this?

(And no, "pull blasters and/or melee weapons" is not an answer that furthers this discussion...)

I think it depends entirely on how challenging such an encounter should be, regardless of what the rules in the book say.

Do you think a Stormtrooper knows how to throw a punch? Does it seems silly that an elite soldier would not have hand-to-hand training of any kind? Sure does to me.

So, use your judgement, I say. Add one or two upgrades to their rolls, so long as it doesn't completely overpower your PCs. Unless that's what you want, then completely overpower your PCs.

If you know that the encounter is going to feature a need for a skill the minions don't have, then you have a few choices:

1a) Play the minions as written without the skill.

1b) Play the minions as written without the skill, but don't use groups and have them use Assist to help one another.

2) Add that skill to the minions.

3) Have a Rival or Nemesis there that can handle the task (not really relevant to a big brawl).

1b) Can work OK for the purposes of a brawl with stormtroopers. They would each have GGG before Aim or Assist is considered. This isn't actually too bad except against dedicated hand-to-hand combatants.

Happy's 1b is the most straight forward answer.

Though depending on the situation a narrative skill challenge type operations similar to those from D&D 4e might actually work smoother then trying to roll out every bar patron, and track every wound.

Yeah. My instinct, short of making any changes to their statblock, is to break them out so as to no longer be a "group". That way, they each have their separate Brawn and go from there. The minion rules do make it clear they can exist outside of being lumped into groups...

This is just blind curiosity, but how off duty are these Stormtroopers? Are they in plain clothes (without their armor)?