Looked up "Out of Arena" "Out of Brawler's guild" and "Brawler's guild glitch" but couldn't find it posted anywhere. Without further ado --
1. Locate the chair shown in the picture. (Its the one facing away from the arena, closest to the wall, on the set of 4 chairs.
2. Strife left, and you'll fall into an instanced Orgrimmar. Make sure you're at 80%+ hp.
3. Mount up (Ground mounts only) and locate an elevator, you should end up where the flight master/trainer is.
4. Follow the directions in the pictures, end up on the ledge facing the Brawlers Guild Hut. On your way to the ledge you may glitch in and out of the arena, ignore that.
5. Jump! Make sure to be ready to click off your paracute, levitate, slowfall ect. Click it off as soon as you're inside the arena.
6. Have fun exploring!
#1 http://imgur.com/O7VIE
#2 http://imgur.com/YrTis
#3 http://imgur.com/4Hdi6
#4 http://imgur.com/OR5n9
#5 http://imgur.com/38ey2
#6 http://imgur.com/RaRjB
#7 http://imgur.com/bye1o