Any time you win on LIVE or locally, it will count towards this achievement. The easiest way to get this achievement is with a second controller. Set up a local game, sign the second account in and just play Original Connect 4. Have the second controller place chips away from yours as you go for Connect 4's. It takes about 15 seconds a game, so that's under 13 minutes of actual game play for 50 wins. You can check how many wins you have by selecting Achievements in the Trophies section of the game.