Major League Baseball 2K10

An easy way i found to do this, without being very time consuming, is play as a good team. Myself being a Yankee fan, I chose them. Basically then, I started up 20 games and before the first pitch I went into the game menu and chose the Super Sim option. Super Sim will count as playing the complete game. Do this for twenty games and sim the rest of the season (making sure you are winning the majority of the games, therefore making the playoffs). I simmed the whole playoffs and won the world series. Make sure you save regularly because if you lose a series or an important game you can just exit out and load up the franchise again.
*Blink* Achievement unlocked

you can just start up a franchise game and supersim through to the end of it and itll count as a played game. just do that twenty times. pick a good team though, just to make sure that youll make the playoffs.

Set to 3 inning games to play your 20. Turn autosave off from the main menu and simulate. If you make any changes to your roster or other franchise options it will save. If you don't win, you can just quit out of the franchise and it won't save.