Return 5 flags in a single battle. This is truly one of the more challenging Achievements among all the Battleground one as it requires a great amount of luck, skill, and a decent connection. You must return your team's flag yourself, which necessitates superior clicking skills. Aside from the difficulty of taking down an enemy flag carrier, you're also competing with your teammates to be the first to return the flag. Now try to do this five times, and you can imagine all sorts of things going wrong. One techinique by which to unlock this Achievement is to simply wait for the flag carrier to die, focusing on the flag return rather than actually killing the carrier. Taking down solo flag carriers on your own is a guaranteed return, as well.
Return 50 flags. This Achievement is just a matter of... persistence. Play enough games of Warsong Gulch while keeping the objectives in mind, you'll be able to unlock this Achievement over time. In fact, constantly trying to complete Frenzied Defender should take you some way towards completing this.
Warsong Gulch Perfection
Win 3-0. The great thing about Warsong Gulch is that it's a perfectly balanced Battleground, and there will be streaks of wins and sometimes streaks of losses in any Battlegroup. If you manage to get lucky with a good match-up -- say the opposing side has no healers and you've got more than a few -- you're virtually guaranteed a shutout. In your journey to 100 wins, more than a few are guaranteed to be perfect. You just need three captures, after all.
Win in under 7 minutes. The only way to get this Achievement is if your team plays to, well, perfection. This means that one runner is ready to pick up the flag as soon as it respawns. It takes 20 seconds for the flag to spawn after a capture, so there's about 40 seconds of dead time. You'll need some fast runners -- as mentioned, like Druids -- in order to optimize travel time and finally, you'll need to encounter minimal resistance and not have your team's flag get too far. If your enemies put up even a token fight, keeping the flag for some length of time, you'll easily go over the 7 minute mark which doesn't include the 2 minute preparation period. Alternately, if the Battleground closes early due to not having enough players (5 minute timer), all you need to do is have one capture over the opponent to unlock this Achievement.
Capture the flag 3 times without dying. Sounds like a difficult Achievement until you realize you don't need to be the one to grab the flag from the enemy base. Another players can drop or pass the flag and it would still count towards the Achievement. This requires that players not die throughout the entire match so while it's easier for some classes and specs, it's quite doable by anybody with the right assistance and circumstance.
Warsong Outrider / Silverwing Sentinel
Gain Exalted reputation with the Warsong Outriders or Silverwing Sentinels. More than anything, this is quite a painful grind for any player starting from scratch. If your team loses without capturing a single flag, you gain 0 reputation. Even if you fought tooth and nail for hours. Old school players have it easier, as Marks of Honor were once turned in for reputation gains. At 35 reputation per flag capture, it will take 1,200 flag captures to move from Neutral to Exalted (less during the Holiday, as it is 35+10 per flag capture). That's a hell of a lot of games. The only upside is that unlike some factions, there's no limit to the reputation you can gain per day. Theoretically, you can play (and win) all day and gain quite a bit of reputation. Good luck.
Not In My House
Kill 2 flag carriers before they leave the flag room. This Achievement was unnecessarily nerfed (it used to require 10 kills), making it ridiculously easy to obtain as long as your team prepares a dedicated defense. The only technicality that needs to be paid attention to is that the 'flag room' in question is exactly the floor where players spawn. Once flag carriers step into the tunnel or outside the door leading to the Graveyard, they will not count towards the Achievement. Players also do not need to make the killing blow, simply have the Honorable Kill count.
Grab and capture the flag in under 75 seconds. This is a truly challenging Achievement that very few players will unlock by accident. Traveling from the enemy flag room to your team's flag room in under 75 seconds will require both speed boots as well as an additional boost from another source such as Swiftness Potions or abilities like Sprint. It also requires absolutely no contestation whatsoever and naturally your team's flag firmly in place. More than the other Achievements, this takes some planning and a confluence of good events.
Kill 100 flag carriers. Easy as pie. Simply help in taking down flag carriers and you should unlock this Achievement after a few days of playing. You don't have to make the killing blow for this to count, either, so this should come naturally on your way to 100 wins or Exalted.
Save the Day
Kill the enemy flag carrier right before they capture the flag. The wording is actually more complicated than that but essentially, you'll need to kill the enemy flag carrier while they're already inside their flag room moments away from capturing your flag. This is hard. The proper thing to do would be to grab the enemy flag in order to delay the cap long enough to kill the carrier. Not grabbing the flag is extremely risky, which makes this Achievement rather challenging. A plethora of stuns, roots, and snares should help you out here.
There you have it. All the Achievements required for the Master of Warsong Gulch meta, which in turn is required for the Battlemaster meta. This Achievement is arguably one of the most fun and challenging Achievements to pursue, requiring a bit of dedication and a real focus on the goals of the Battleground. None of these Achievements are purely random, although it's quite possible to get a few by accident. Nonetheless, the road to Master of Warsong Gulch is long and fun. As a last note, don't forget to do Not So Fast, which requires you to kill a player who has the speed boost. It's not required for the meta, but it's always fun to mow down a sprinter.