River City Girls 2

Basically, it's completing a side quest.

First one is to help Sayoko "train" some Male Students in Volleyball. You'll find her at a ball court to the left of River City High, in Crosstown. I found it after beating the first boss (Ken) at the mall. You'll get a text from Sayoko asking for help. Go to your phone, highlight her text and hit A, to show the location on your GPS to follow.

Talk to Sayoko and agree to help. You'll be up against 6 Male Students and have 3 Balls to use after hey try throwing them at you (You cannot hit them unless you throw the balls at them). You and the Males have 3 hearts each, and the Males can hurt each other and you, which helps somewhat. You lose all 3 hearts; you lose and have to try again.

Once all 6 are defeated, you earn some XP and some money, and the achievement should pop.

Good hunting!