Legit : If you want to do this achievement legit there are a few things I suggest you do.
1. Stay away from CAFS. Usually they are stack with 100 everything.
2. Stay away from people with good records.
3. Dont toy with anyone. Flash KO's do happen and are extremely frustrating. Remember, youre going for wins not XP.
4. Pick or stay away from Damien Maia. His submissions are crazy. If you get matched up with someone in middleweight and they pick Maia. There is a good chance they will try to submit you early.
1. Pick Middle or Heavy Weight.
2. The Winner pick Damien Maia or Frank Mir. Noguira would also work for Heavyweight.
3.Meet in the center of the Octagon and hold the LB and push the right stick towards your opponent. (You should be single collar clinched)
4. Click the LB and Right Stick. (Pulls the flying Armbar)
5. Your partner should let you submit them.
This is the quickest method.
-Hope this helps.