Just a quick note/warning about this achievement:
It seems as if some people are having an issue with the achievement locking up at 30%, hence making it unobtainable for them. I'm assuming this will be patched later on but be warned.
As stated in the description, all you need to do is score or assist in 30 goals. This does not have to be done in one game and it has to be done in any online matchmaking game (this includes specialty games such as Hoops and Dropshot). I personally recommend solo 1v1 games as you usually get 5 or more goals a game.
For the majority of you who have already completed this prior to the update, you do have to score/assist 30 more goals as any previous progress does not count.