This grindy trophy will take a while, but it's not that hard.

The time it takes mostly depends on how much you play, since one game takes roughly 10 minutes from start to finish. To cut down on the time, if you are losing by more than 10 with less than a minute to play, it's probably a good idea to forfeit, or, if you know the team you are playing is much higher level than you, forfeit as soon as possible. There's no use wasting time just to lose a game unless you are trying to complete a specific solo quest, however, keep in mind the game does require at least 2 of the 3 players on the team to forfeit though. If you are winning by a good margin, just hang on to the ball for the full 24 second shot clock and take a shot at the last second. Putting up more shots prolongs the game as the timer stops after each made basket.

You can keep track of your Total Wins by pressing Options>Management>Stats>User Stats>3vs3>Total. Once you win your 300th Match the trophy will pop.