To start a Be A Pro game go to "Main Menu">"Game Modes">"Be A Pro". Now when you click on that a page should come up telling you what everything means. The very first thing it will show and tell you is how the Performance Bar works, that is how you get this achievement. You will need to get that Performance Bar at least 3/4 of the way full to get an 80 rating. By Scoring points, getting Rebounds, getting assists, getting steals/blocks and playing good Defense will all help you towards getting this achievement.