Titanfall

You need to be on the winning team of an Attrition match 50 times. Note that for the "I've Seen It All" achievement, you also need to play Attrition on every non-DLC map at least once, and for various DLC achievements you will need to play this game mode on every DLC map as well.

The Campaign playlist has quite a few games that are Attrition matches, and those count for this achievement. Since you need to win all of those for other achievements, I suggest completing all of the Campaign achievements before focusing on this one.

This achievement can be tracked in the Player Stats -> Levels screen, although it shows win counts by map so you will have to scroll through all 24 maps and add up the total yourself. You also can look at the achievement app where each 2% equals one win.

Boosting Method:
Attrition is by far the most popular game mode, and even the Asian servers usually have 50-100 players active at any given time as of April 2016. As such, boosting is problematical and unlikely to work without 12 players. Create a twelve player game on one of the Asian servers and have the losing team all run to a clear central spot to be killed by the winning team. You cannot use the quit method due to the popularity of the playlist. While a victory would indeed be counted if all opposing players quit, chances are high that a random player would enter the game on that team before the game registered a victory.

Non-Boosting Method:
You are much more likely to win in a competitive Attrition match if you have a few teammates that have mics and coordinate. Killing Pilots and Titans are four points each, while killing grunts and Spectres are one point each. If you struggle with keeping a positive k/d ratio against enemy Pilots, focus on mopping up lots of one point kills. Using the Smart Pistol it is quite possible to kill 40-60 grunts and Spectres in one game, which is enough points to positively contribute toward a team win even if you get killed 6-8 times.