This trophy is titled "Legionnaire" and it's for reaching level 10 in online versus. Points are gained in both victory and defeat, however when you lose the points are next to nothing. Winning against higher levels warrants more points, however if you're planning on going through this multiplayer with a friend you'll both be able to rank each other up fairly quickly. It's strongly recommended you play in Ranked Matches given the fact more exp is warranted there, however you can also get points in player matches which helps. Level 10 is fairly early on, however there is also a trophy for level 30 which is a bit more of a grind.