Taken from the Burning Wheel Forums, by Luke:
Folks are always asking how to run a melee in BW involving more than two combatants. I thought I'd offer some insight.
The advice I give below is for running 3 to 6 PCs vs 3 to 10 or so NPCs. For bigger battles, I strongly urge you to use the Bloody Versus test rules. Why? Because life and death struggle in Burning Wheel should be personal. Large groups are impersonal and not conducive to making vital decisions about personal Beliefs RIGHT NOW.
Martial Actions all behave the same, whether you're fighting one on one or three on one. A Block only works against one incoming Strike. Great Strike only hits one target. Etc.
Avoid is the only action that works against multiple incoming attacks. If a player Avoids on action 1, his Avoid successes count against all incoming attacks on action 1.
If two people Strike me, I'm screwed
Yes. If your character is the target of two incoming Strikes on action 1, you're likely in trouble.
Can I divide my dice? Optional Rule
Block, Strike, and Counterstrike can be set to affect multiple actions/targets. Using this optional rule, players may divide their dice for their action between multiple targets. As with Counterstrike, all dice must be divided before anything is rolled for.
Will this break the game? No. But it takes away a level of grit and consequence. The game takes on a slightly more Pulpy, John Carter of Mars feel. (Well not quite. But kind of.)
Can I Block a Strike against the Prince?
Players are forever trying to protect their liege lords from harm. I allow players to Block or Counterstrike blows at another character at a +2 Ob.
Position to your heart's content
Positioning really shines in big melees. You can position your character so you're in optimal striking distance for one enemy, but out of reach of another.
Intent is key here. It's vital that players be clear with what they want out of every positioning test. You can position against any and all of your opponents. But each opponent you include in your intent can position against you, too.
After intents are laid out, roll the dice. Layout the number of successes, from highest to lowest. Highest gets his intent unsullied by anyone else's. Everyone else is going to beat one character, but lose to another.
For example: Luke, Dro and Thor are fighting. Luke Maintains against Dro with 8 successes. Dro Closes on Luke with 4 successes. Thor Closes on Dro with 5 successes.
Result? That's easy. Thor Closes with Dro. His relative position to Luke doesn't change.
That's another trick. If someone isn't included in your intent, then you don't change your distance from him. If you haven't positioned against a character in the combat yet, use a little a common sense for starting relative position. However, I generally make players make a new positioning test.
For example, the Dwarven Prince, Dwarven Warden, Elven Prince, and Elven Captain have come to blows. Again.
The D Prince and Warden go great guns against the E Prince. They ignore the Captain. The Captain guns for the D Prince. The E Prince withdraws successfully, leaving the Warden out in the cold. Where is the Warden in relation to the Captain? Can he Strike him? I dunno! A positioning test is called for to find out where he ended up in the whirlwind melee.
A final note: It's very tempting to get precise and exacting with positioning in big melees. Don't. Don't sweat the small stuff -- if two characters haven't been positioning against each other, then they're not in range to strike. And if there's ever a question about where characters are, either use the current positioning test successes -- whoever got higher gets his intent -- or just make a new positioning test and go from there.
A Little Help Please!
Use the helping rules in combat. Use them often. Characters may help each other with positioning tests and nearly any action in the script. I usually restrict players from helping each other with Strikes or Natural Defenses. But that's about it.
Of course, the same action must be scripted at the same time in order for help to be possible. On the other hand, I'm a bit more generous with positioning tests. I allow "I'll hold 'em off! You run!" helping -- I Maintain, you Withdraw. We both make one test against the mad Captain.
Check out the extended example