SEGA Superstars Tennis

You can unlock courts by progressing through Superstars mode from the main menu the names of the courses and how to unlock them are listed below-

Note* If you play through the game you will eventually get this anyway its hard not too.

Jet Set Radio Course: - Play through the jet set radio level until you get to the mini-game that has you playing a tennis match against Beat, which is the 6th mini-game. Win this match and you will unlock the course.

Nights Course: - Play the Nights level in Superstars mode and win the first mini-game, which is a doubles tournament, to unlock this course.

Outrun Course: - Play the Outrun level in Superstars mode, and win the first mini-game, which is a doubles match, to unlock this course.

Sonic The Hedgehog Course: - Play the Sonic the Hedgehog level in Superstars mode, and win the eighth mini-game, which is a single match, to unlock this course.

After Burner Course: - Play the After Burner level in Superstars mode, and win the first and only mini-game, which is a singles tournament, to unlock this course.

If you find this solution to be unhelpful, please tell me why in a comment and I will update it the next time I'm online.