Instructions
Hold the Right Trigger on your Xbox or Xbox 360 controller. On the PlayStation 2, hold the R1 button.
Press the Y button for Xbox or the Triangle button for the PlayStation 2 to jump while continuing to hold the Right Trigger or R1 button.
Rotate the right analog stick on any of the controllers clockwise for two rotations. Timing is key; do this quickly to make the dunk.
Press the Y or Triangle button again to complete the dunk.