Boom Robots

To get this achievement you must win a game by playing a solo game without any controllers plugged in. Start a game from the main menu by selecting Play and pick any of the options. 2 vs 2, 3 vs 3 or 4 vs 4. Win a round by yourself with all AI and you'll earn this achievement.

Pretty easy, but I couldn't figure out why this wasn't popping as I was playing with extra controllers for the other achievements.