You can get this by playing Postseason Mode. Select New Postseason from the Main Menu. Pick any team and you'll first have to play a Wild Card game (make sure you win) and then you'll advance to the divisional round and have to play a best of 5 series in which you must 3 of the 5 games. Once you have done that, you will get this trophy. Make sure you actually play the games and don't sim. You can put the difficulty on easy and the fielding on assisted as well to help make it easier.
If you're struggling to win games, you can dashboard and quit the game anytime something bad is about to happen like giving up a home run. If you're fast enough, when you load back into the game you'll be able to resume right where you left off as the game auto-saves after every pitch and every play.