Quickest way to get this, is to start a new season from the main menu. Select short season (16 games and playoffs will be a best of 3) Set ego to 0. As for team, I used the Sirloins, but any team should do. Don't worry if you lose a Game or two as you should still be able to qualify for the playoffs. I lost my very first game 1-0 because I could not get the hang of the hitting, lol.
If things start going bad in a game, don't quit out! If you do, you will receive an automatic loss! On 0 ego, if you get down by 3 or 4 runs, you should be able to come back pretty easily, once you have the hitting down.
By the time you get to the playoffs you should be dominating every game. You will play a best of 3, first round series against another team in your division. You can lose a Game and still win the series. I did sweep 2 games and moved on to the championship.
Same thing for the championship. You will play the winner from the other conference. Its a best of 3 series. Win 2 games and boom, you are the champion. Achievement should pop at the conclusion of the game.