Instructions
Select a team with at least one player on it with a high dunk rating. For example, Shaquille O'Neal, Kevin Garnett and LeBron James all have excellent dunk ratings.
Press and hold either the "L1" or "L2" button while you have the ball in your own end to go into "Turbo" mode. This will let you briefly run more quickly and will make your dunks more accurate.
Run up to the basket using the left joystick. Hold down the "Square" button to perform a dunk, then release "Square" just as you dunk the ball. There is a random chance of the backboard breaking.
Go under the basket in your own end if you don't have the ball. Press the "Triangle" button to call for the pass, then tap the "Square" button to jump up for the alley oop pass. Press "Up" on the right joystick after you catch the pass to finish the alley oop.