This trophy, like the others, can be earned without an opponent. Unfortunately,
it must be earned in a public match, not private, so staying alone isn't guaranteed. Just start a 1v1, pick a nice easy map (such as the first one or the sand one) and start whacking them in. You can just score from the start each time, allowing you to rack up the points.
With a bit of focused effort you can get around 50 goals a game, or 30 if you're playing lazily. My record was 65 in one game, if you're looking for a challenge!
Doing this trophy will also give you wins progressing towards the Victorious trophy, which is a nice bonus!
That being said, this game really comes into its own with the online play, so make sure you enjoy it!