I don't know if this has been posted but here It can't be done in private matches. What you do is 1. You and a friend join a KOTH game together. You'll both be on the same team of course. 2. One of you quits to main menu. 3. Send a friend request to anyone on the opposing team. 4. Whether they accept the friend request or not you can press X and join their game! You and your friend will now be on different teams in the same game. 5. Cancel friend request and start executing. Credits goes to this guy: rubens34 @XBOX360Achievements for the share. Source