Instructions
Run "NBA 2K10," and pull up the navigation menu.
Click "Game Modes" followed by "NBA Blacktop." Select "Dunk Contest" from the list of available game modes.
Select four players for the dunk contest. The first player will be you. In single-player mode, the other three players will be played by the computers. Press the indicated button to start the contest.
Earn the Dunk Off achievement by winning the dunk contest. You have three dunks per round, with one replacement dunk. At the end of the round, the lowest-scoring player is eliminated. After three rounds, the one remaining player is the winner.