Mortal Kombat 1

Under Versus>Online, the option under Ranked is Kombat League. This is the ranked multiplayer mode where you will ideally face opponents of similar skill, and you can earn rewards as you rank up.

For this achievement, you need to complete five "sets" of Kombat League matches. A set is a best-of-three series against the same opponent.

What this achievement should really say is "Lose 10 Kombat League matches" because that's honestly what it will take to unlock this. As I said, a set is a best of three matches, so you have to keep fighting the same opponent to complete the set. However, the loser of each match gets to choose how to proceed, whether that is to continue the set, choose a new character or quit to the main menu. It is all too common for people to leave after the first match if they lose, if they didn't already quit during the middle of it. If you or your opponent leaves before the set is complete, it doesn't count for the achievement, though it will still register under your Kombat Stats.

If you just let the opponent beat you, and then select Rematch, you can get a set done in just two fights. At lower ranks this will not deduct points from your rank progress, but it will obviously count as a loss on your record.

Once you get to the set results screen you should see the achievement tracker tick up.