This trophy is titled "You Brute!" and it's for winning three consecutive ranked matches. In order to play in ranked matches, you must go over to the network tab from the main menu and select it. Proceed to choose ranked matches and do a quick search, the only quirk here is you either have to beat a random (which will be tough to come by, even if you do chances are they are very skilled.) or have a friend pair up with you. Regardless, the trophy will pop at the end of a match you have won in the post battle screen after your third win. Strongly suggested that you find a partner via the boosting sessions as a streak can be a tough thing to keep.