Ozci221,118 Locked 06 Jan 2016
*(This method uses atleast one extra controller)*
Start up ARCADE PLAY. Choose your team (I think any characters work, I chose Terry, Andy and Joe).
Press Start on your second controller or keyboard (default for keyboard is "E"). Choose Choi and any other two characters. Go all the way to the left with both characters. Start tripping Player 1 (in my case Terry) using Player 2 (Choi). Keep doing it untill you stun Player 1. Once you're stunned, press LB (L1) or whatever your binding for LP+LK+SP is. You will now perform an assist attack and unlock the achievement.