The trophy description states that you need to fight five different friends in Infrastructure in less than one hour.
However, this is not entirely true as there are two major work-arounds that will make this easier than it seems:
- You don't have to fight friends only. You can even fight with randoms. Wins earned against randoms count towards this trophy aswell. Change your character's fighting style to "boxer" using "touch controls", this makes things easier aswell if you haven't changed it so far.
- You can adjust your clock in PS VITA System Settings to stay in the "one hour" timeframe. All you have to do is remember the first time you actually won a match in Infrastructure, and the next time you fight again or boost just adjust the time close to the day and time you won for the first time.
So, if you don't want to gather 5 people in order to boost this trophy you can try your luck online. The MP is populated - even tho the number is small - most likely because this has gone free with the PS Plus line-up.