This is a simple achievement to get. All you have to do is beat another player online in a ranked match with a team of generic players.
The amateurs in this game are:
1. All Rounder
2. Power Hitter
3. Contact Hitter
4. Power Pitcher
5. Control Pitcher
6. Star Fielder
Since there is no online community this is easily boosted since its not difficult to be matched up with your boosting partner.
Go for Shut'Em Down as well when getting this to get both online achievements out of the way at once.