Blitz The League

Simple, if not a little time consuming. I believe there are 20 teams in the team selection screen, but if you set the games to one-minute quarters you can probably knock this off in a little over 4 hours (roughly 15 minutes per game including load times).

Simply start with one team and each game, advance through the roster. Cincinnati is a pretty easy team to beat, so choose them for your opponent and you should pretty much win every game if you have already gotten familiar with the controls and the gameplay.

Once you win with the last team, the Achievement will unlock when you hit the Post-Game wrap screen.

Be forewarned, as PunkRawkSoldier pointed out in the comments, if you have cheats enabled it may prevent the Achievement from unlocking.

I found out the hard way that the quick play games all need to be done in one sitting. I had been doing a few a day, and saving everything, but the achievement didn't pop. I ended up having to replay the games from previous days, and everything finally popped. Not sure if it was just being glitchy for me, but I would suggest just doing them all at once to be sure.