You must play Quick Ranked matches to earn this Achievement. That makes it a little trickier for boosting, since you can't see your opponent's Gamertag until you are in the match. I suggest joining a Party with your boosting partner and ensure that you are matched with each other (based on team selection) before you start the match. If you don't have a headset, arrange to always pick the same two teams against each other - it's cumbersome but effective.
After throwing the first pitch, have your opponent select Quit from the pause menu. Respond to the prompt that you do not agree to let your opponent quit the match (choose "NO"), and have your opponent respond to the following prompt that he wants to quit anyways (choose "Yes"). You will get credit for the win.
Repeat this step five times to earn your 5-game streak. Then be a good sport and return the favour to your boosting partner. Knock this one out of the way en route to your 10, 20, and 50-win Achievements. After you each have your 5-game streak, you can just alternate wins until you both reach 50.