This achievement can be obtained legitimately by winning 100 total games in Xbox Live Ranked matches. If you’re new to the game, be prepared to lose quite frequently because many of the players who still play online are very good. It is also possible to obtain this achievement by boosting with a friend. Simply have one person host the game and the second person keeps searching for a Ranked Match until they find the first person. At that point, load up the game and one person lets the other win. Repeat two hundred total times, alternating victories, and both of you will unlock the achievement.
If that takes too much time, Link2430 reported that it also counts as a win if one person simply quits out once you both get to the character selection screen. Either way, the ease with which you can find each other depends entirely on how many people are online at a given time. If you’re on during peak hours, it can be frustrating, but if it’s a slow day, you can finish a match every couple of minutes.