Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Free Throw (25 points): Defeat Episode 1.
Jump Shot (25 points): Defeat Episode 2.
3-Pointer (25 points): Defeat Episode 3.
Dynasty! (40 points): Defeat Episode 4.
Legend! (50 points): Defeat Episode 5.
Hall-of-Fame! (200 points): Defeat Episode 6.
Can't Stop the Reign (100 points): Unlock all Super Dunks.
Double Double (100 points): Defeat every Episode of Story Mode twice.
Takin' it Downtown (10 points): Win Your First Ranked Match on Xbox LIVE.
Getting Into It (25 points): Win 5 Ranked Matches.
Dedicated (100 points): Win 25 Ranked Matches.
Show-n-Prove (25 points): Perform a Shut 'Em Down Move in a Ranked Match.
Achiever (25 points): Perform a Level 3 Shut 'Em Down Move in any Ranked Match.
Big Air (50 points): Make a 3-pt. Shot in a 2v2 match beyond the Half-Court Line in Single Player Game Modes.
Show Off! (100 points): Perform a Level 3 Shut 'Em Down Move in a Single Match in Single Player Game Modes.
Pass the Rock! (20 points): Complete an Alley-Oop from your Pass-To Buddy in a Single Player 1v1 or Xbox LIVE Match.
Just Getting Started (20 points): Complete Your First Chapter of Story Mode.
Own the Court (50 points): Perform a 7-Move Combo String in Single Player Game Modes.

Additionally, there are two secret achievements:

Loser (0 points): Lose 5 consecutive Ranked Matches.
Respect (10 points): Watch the credits movie in its entirety.