The scene: This is a 10 versus 10 battleground that takes place on the border between Ashenvale Forest and the Barrens. If you are Alliance, you enter into Silverwing Hold, bastion of the Silverwing Sentinels, and if you are Horde, you enter into the Warsong Lumber Mill. These fortresses are located at opposite ends of a large rectangular map, with a wide field in between them. Also present are four small houses, two on each side of the respective holds. In one house is a buff which enables a character to go berserk--they do more damage, but they take more damage as well. In the other house is a buff which restores health and mana. These respawn constantly throughout the game.
The objective: Inside each fortress is a flag--your task is to take that flag and bring it back to your base 3 times. Whichever side accomplishes this first wins.
The first thing to understand is that you cannot capture the flag if your own flag is not in its pedestal. Therefore, if you successfully take your enemy's flag and escape to the base, but one of your enemies has yours, you will have to kill the person with your flag before you can capture theirs.
What usually happens at the outset of a Warsong Gulch game is that all 10 players of either faction leave the base, mount up, and go for the flag. Then, the two teams clash in the middle on the way back. This is where things can fall apart, because many players do not understand the concept of the Assist Train.
An Assist Train is when 9 players are focused on helping the Flag Carrier reach the base -as well as- dismantling the other team's train. When you have two skilled teams, this can be -very- difficult. Knowing what to do is a question of knowing your class's abilities as they relate to protecting your carrier and dismantling your enemies. For example, a Hunter might set down freezing traps to slow enemies trying to attack the Carrier as he runs, and might additionally use their ranged power to slow the opposing team's Carrier and/or slow/kill the healers. Similarly, a rogue can gouge, sap, and flat out stunlock an FC/healer, a mage can frost nova/blow people up/sheep, etc. One key aspect of flag carrying is that paladins can cast Blessing of Freedom on he carrier--this is extremely useful (in lieu of that, people are also fond of free action potions. Or they are druids.).
It does not ultimately matter which class chooses to carry--I've seen every class do it successfully--but by far the most caps are made by Druids, Rogues, and to a lesser extent, Warriors. Warriors are easier to heal, but they move slowly and are susceptible to a mage's burst damage. Even with numerous healers on him, a warrior cannot survive a multimage assault. Druids and Rogues succeed by avoiding the enemy altogether. They go travel form/sprint. Continuous movement is important--you MUST NOT stop to fight, you must RUN. This is where the problem lies for many pick ups.
At most, three people should support the carrier entirely once the teams clash in the middle. The rest of the team should break away and kill the opposing team's carrier. If this is not possible, then they should leave off once the enemy enters its base's tunnel and support their own carrier, then decide a plan of attack for retrieving the flag. The flag carrier MUST NOT be left alone. How you divide the responsibility of offense and defense is up to you, and should be based on class and circumstances. Generally people prefer to split the team in half, but sometimes uneven distribution is required. It depends on who you're fighting.
Again, you must be mindful of changes in 'pressure'--if the enemy sends 7 players to destroy your FC, that means only three are back protecting yours. When you notice such a big incoming, you should take your people to eliminate the enemy FC, so that even if your FC dies, they still don't score.
--Don't take berserker if you intend to carry the flag. Seriously.
--In each base's tunnel there is a cul-de-sac which contains a pair of speed boots. Do NOT use these boots if your carrier is coming up the tunnel and needs them to sprint to the pedestal. DO use them if the FC is nowhere near the tunnel, as this prevents the enemy making use of them.
--When carrying the flag, anything you do to make yourself invulnerable or impossible to target will cause you to drop it. This includes Feign Death, Iceblock, Vanish, and the paladin's Divine Shield. Sometimes carriers use this strategically--they Vanish to drop target and pick up immediately afterwards. But exercise caution.
--As with other BG, the key is to communicate. Let people know what's going on. Stick together. Stay organized.
Warsong Gulch is a very difficult battleground to master, but once you've got the hang of it, it's wicked fun--and excellent honor.