The general idea

Ultimate Team Cardboard Fortress Battle (UTCFB). It's a long name, but those five words manage to both name and describe this game, which is an inexpensive and almost unreasonably entertaining combination of:

Arts & crafts
Real-time strategy
Full-contact sport

There are two teams:

Each team has a General.
Each team builds their own Fort out of cardboard boxes, hiding a Flag inside one of the boxes.
Each team must destroy the other team's Fort and capture their Flag.

Playing the game

Here's how it goes down:

On the appointed day and time, everybody shows up.
Flattened boxes are assembled.
Boxes are split into two piles.
Two teams are chosen.
Generals are chosen, by whichever method seems appropriate.
From the two piles, the teams construct their Forts, and hide their Flag in each.
When Forts are complete, the two teams meet in the middle of the field and sit down.
Each General delivers a two-minute Braveheart-style battlefield address to their troops.
The two teams return to their Forts.
Game on.
Battle goes in rounds: five minutes on, five minutes off, until the victory conditions are satisfied.
Victory conditions are satisfied; glory to the victors, honor in defeat to the vanquished.
Cleanup time. Or play again, if everyone's up for it. Then cleanup time.
(optional) Party.

What you need

Here's what you need to be ready for battle:

People

At least twelve people, total, must be playing. The smallest number of people per team is debatable, but fewer than six is probably going to give you problems.

"The more the merrier" absolutely applies in Ultimate Team Cardboard Fortress Battle.

Supplies

There are two categories of supplies. Fortunately, they're both easy.

Things everyone needs to bring

Wear clothes you can get dirty. The word "battle" is in the name for a reason!

Everybody who shows up must bring the following things:

A white t-shirt
A colored t-shirt
As many flattened cardboard boxes as you can carry
At least two rolls of wide masking tape or packing tape

Don't bring duct tape; too hard to destroy

Things one person needs to bring

One person should be responsible for bringing some other stuff, which breaks down into two categories:

Battle-related items

For the Generals:

At least three athletic whistles
At least two hats of proper distinctiveness

As Flags:

At least two easily-recognizable scraps of cloth

If the Converter variation is being considered:

At least two headbands

For the teams:

Two stuffed animal mascots of reasonable size, one for each team

Logistical support

For cleanup:

Lots of twine and a couple pairs of scissors

Just in case:

A first aid kit

Where to play

Is there a big field in your town? Go there. You're gonna need space.

Roles

Everyone on the field will fit comfortably into one of these roles.

Noncombatants

There will always be those who stand and watch. Those people are needed to do a few things:

Timekeeper. Someone needs to make sure battle goes in rounds of five (5) minutes, and that there's a five (5) minute break in between each round. Give this person an athletic whistle.
Penalty Box Watcher. Someone needs to make sure people are doing their count of 120 when they're in the penalty box, which is explained below.
Stuff Watcher. Before battle begins, all combatants have to shed their glasses, watches, wallets, cellphones, and anything else that could get broken or messed up. All that stuff will probably go into a pile that someone should keep an eye on.
Action Photographer(s). The more of these there are, the better.
Battle Referee(s). If the game is big enough, some people may take it upon themselves to roam the field and make sure the opposing armies battle with honor -- no illegal moves, observing the 3-count, going to the penalty box, etc. UTCFB doesn't need these refs, strictly speaking, but sometimes they're nice to have around.

Combatants

We few, we happy few, we band of brothers;

For he today that sheds his blood with me

Shall be my brother; be he ne'er so vile,

This day shall gentle his condition:

And gentlemen in England now a-bed

Shall think themselves accursed they were not here,

And hold their manhoods cheap whilst any speaks

That fought with us upon Saint Crispin's day.

- King Henry V, Shakespeare, Henry V (IV, 3)

Both teams should be composed of equals in rank and number, except for one person: the General.

The General

The General is basically the team captain, and is free to lead their team in whatever way they desire.

Before battle begins, Generals should be issued a hat and an athletic whistle.

The General's only formal duty is to wear the hat and deliver the pre-battle speech before their team.

The pre-battle speech is non-negotiable; any General unwilling to do the speech must relinquish their office to a worthier teammate.
The pre-battle speech need not necessarily be original material.
The only requirement is that it be awesome.

In battle, the General differs from the rest of the team in only one way: if the General is tackled and pinned for the required 3-count, the round ends instantly. The General should then blow their whistle, signaling the end of the round. At that point, the five-minute break period begins before another round can start.

Rules

There are only a few sets of rules:

Rules of battle
Rules of the Fort
Rules of the Flag

Rules of battle

Each team must prevent the destruction of its Fort and the theft of its Flag by defeating the other team.

These are the rules of battle (they're pretty much just simple common sense):

The first rule of UTCFB can be summed up in Wheaton's Law: Don't be a dick.

Sometimes people can get competitive. This is a fine thing to see in sports, but remember that your teammates and enemies are here for fun first and foremost. The first rule of battle is the first rule for a reason.

Battle consists of tackling and grappling; the goal is to pin someone's shoulders to the ground, face-up, for a 3-count.

A 3-count is counting to three; it does not necessarily mean three whole seconds.
Pinning someone only counts when they're face-up; pinning someone's shoulders to the ground when they're facedown seems kind of stupid and dangerous. Remember the first rule.

Once someone is pinned, they must go to the penalty box for a count of 120.

A combatant on their way to the penalty box should clasp both hands above their head to distinguish themselves from combatants still in play. No one should attack these people. Conversely, combatants who fake this status to get themselves closer to the enemy Fort, while admittedly displaying cunning, are breaking the first rule.
A 120-count is counting to 120; it does not necessarily mean two whole minutes.
When the 120-count is done, the combatant must first touch their own Fort, or the remains thereof, to be considered back in play.

Anyone at anytime can tap out by tapping their opponent twice, or simply saying something along the lines of "I give up!" or "I'm out!" or "I yield!" When this happens, both combatants should disengage immediately and roll off each other like they just found out the other person is made of lava or coated in poison oak. Whoever tapped out should head for the penalty box for the required 120-count.
There is no punching, kicking, slapping, biting, tripping, or anything else unpleasant allowed.

Don't choke people from behind.
Any move where you lift someone bodily off the ground more than a foot should not be considered.
Remember the first rule.

No outside weapons are allowed.
Double-teaming, triple-teaming, or an all-team dogpile are completely permitted strategies as long as nobody gets seriously hurt.
Battle should be self-regulating; all combatants are expected to behave with honor and dignity. Remember the first rule.
If you've pinned somebody for the required 3-count, it is considered sporting to help them up afterward before they make their way to the penalty box.

Rules of the Fort

These are the rules of the Fort:

How you build your Fort is entirely up to your team. These are the permissible materials:
- The cardboard boxes everyone brought, or fragments thereof.
- Masking tape or packing tape.
- Ingenuity and cunning.
During battle, it is forbidden to steal boxes from your enemy's Fort to add to your own.

Rules of the Flag

These are the rules of the Flag:

The Flag cannot be hidden on a team member's person.
The Flag must be hidden somewhere within your Fort.
The Flag cannot be hidden inside a box that's been entirely wrapped in tape, like a mummy.

Before the first round begins, both Flags must be shown to the timekeeper and all combatants, so everybody knows what they're looking for.

Gameplay

Battle lasts for rounds of five (5) minutes, or until the General of a team has been tackled. A noncombatant will usually time the rounds and the breaks; give this person an athletic whistle. To signal the start and end of a round:

Each General should blow their whistle three times to signal their team to get ready.
The Timekeeper should blow their whistle once, long and loud, to begin the round.
And also to end it.

When a round is over, a break period of five (5) minutes begins. Teams can use this time to do what they must, which usually includes:

Taking a breather
Repairing the Fort to the best of their abilities
Hiding the Flag somewhere else
Reformulating battle strategy

The game continues in this manner, alternating between rounds of battle and breaks, until the victory conditions have been satisfied.

Victory conditions

The conditions for victory are simple. Your team has won when:

The enemy Fort is in ruins.
The enemy Flag is in your Fort (or the center of the ruins of your Fort) with your knowledge.

Tackling the General

If the General of a team is tackled and pinned for the required 3-count, the round is over instantly. The General should blow their whistle, battle should cease immediately, and the break period should begin.

When the game is over

After the cessation of battle, both teams are encouraged to form a line behind their General and do that thing where they pass each other and give a series of hi-fives, saying "Good game," because that's what should happen when two worthy teams face each other in battle.

Then it's time to clean up.

Miscellaneous Details

A few miscellaneous details that are good to think about:

Pre-battle prep
The penalty box
Cleaning up afterward

Before battle: what to do with your stuff

Everyone arrives on the field with a bunch of stuff that they shouldn't have on them while battling. This includes:

Glasses
Cellphones
Watches
Wallet
Keys
Jewelry

All that stuff needs to be taken off and put in a safe place that a noncombatant can keep an eye on.

The penalty box

The penalty box should be a spot off to the side of the field, equidistant from the two Forts. Mark the location in whatever fashion seems appropriate and make sure everybody on both teams knows where it is. Upon exiting the penalty box, combatants must first touch their own Fort before reentering battle.

Cleaning up

Before the teams leave the field, everyone should grab twine and scissors and make bundles out of the flattened cardboard boxes that litter the field.

The best way to make a bundle:

Get a large, flat, rectangular piece of cardboard.
Stack some destroyed boxes on one half of the rectangle until you've got a decent-sized stack.
Fold the other half of the rectangle over the stack.
Tie it all up with some twine.

These bundles can be taken to a recycling center, a dumpster, or saved for some unknown bonfire-like purpose.

Optional tweaks and variations

There have been a few tweaks and variations that have been proposed and/or tested; use them or don't. It's a free country.

The Great Outdoor Fight

The Great Outdoor Fight takes place before teams are chosen, and can be used to choose Generals, as well as assess everyone's general battle skills. The Great Outdoor Fight uses the same battle rules as UTCFB proper.

There are no teams.
There's no time limit.
The last person standing wins.

To begin The Great Outdoor Fight:

Everyone stands in a circle facing outward.
Everyone takes ten steps straight ahead.
The whistle blows.
Fight!

The victor may win the right to be a General and choose the opposing General, or simply win the right to choose who both Generals are going to be if s/he doesn't feel like being one. It's up to you.

Sudden death

It's entirely possible that both teams may become exhausted by battle. In this case, sudden death mode can be invoked pending the agreement of both teams and their Generals:

There is no battle in sudden death mode.
Both teams must verify the presence of their own Flag in their Fort, and can take up to five minutes to hide it again if necessary.
Both teams begin the round touching their own Fort.
At the whistle, each team runs to the opposing Fort.
Each team should devote itself utterly to tearing apart the opposing Fort and finding the Flag.
The first team to find the opposing team's Flag and bring it to the center of the field for the timekeeper to verify wins.

More than two Forts

It seems at least theoretically possible to have more than two Forts if the number of expected players is large enough. In this case, all rules are exactly the same, with the following additional tweaks to be considered:

Players should be told to bring shirts of a specific color, i.e. white, blue, black, red. Armbands can also be employed.
The game is over when only one team remains standing with its Flag uncaptured.
Each team should be allies with the team to their left, and enemies with the team to their right.

Maybe? This might be completely nuts. As of the time of this writing, no multi-Fort variation has ever been tried, so this might be a completely unworkable idea. Then again, it might result in glorious chaos, which is always to be favored.

The first team whose Flag is captured is obviously knocked out first. The members of that team become roamers:
- Roamers can't run.
- Roamers don't defend specific Forts.
- Roamers only attack. They attack anyone within their reach.
- Roamers are subject to all rules of battle as normal.

Combatant role: Converters

Converters are a combatant role for UTCFB proper. Each team has one (1) member wearing a headband, known as the Converter. If the Converter tackles and pins you for the requisite 3-count, you are now on his/her team for the duration of the round; don't go to the penalty box -- go change your shirt. Be advised that Converters themselves can also be converted.

Notes

This is a space where some unofficial observations about gameplay can be made.

Tackling the General

This may seem like a nonsense rule at first, but consider the following scenario: your team is getting their ass kicked. The enemy swarms upon your Fort and it seems likely that they'll find your Flag at any moment. You can make them all stop fighting and leave your Fort immediately; all you have to do is tackle and pin their General.

Conversely, your team should be aware who the enemy General is; you may want to consider issuing a standard order not to engage the General in serious battle if things are going well for you -- how you keep the enemy General occupied is up to you.

Double-teaming

This may seem unfair, but consider that any team is likely to have at least one really huge or really tough guy. Nobody is going to be able to deal with that dude singlehandedly; you've got to form a team and take him down, or just keep him busy. It is always possible to do this honorably.

Stuffed animal mascots

These are not strictly necessary, but are kind of great, if only to have something for your team to rally around. You can have White Shirts vs. Colored Shirts or what-have-you, or you can have TEAM TIGER against TEAM HORSE. It's up to you. You can get big, ridiculous stuffed animals from just about any thrift store of worth.

Ultimate Team Cardboard Fortress Battle is � Jon Sung. By agreeing to play by the rules, players acknowledge that they're responsible for their own actions and automatically forfeit the right to sue Jon if someone gets hurt or something. Remember the first rule of UTCFB.