Instructions
Use the left joystick to move your player toward your own basket. To perform an alley oop, it's easier to start from your opponent's end after you get the ball either after the other team scores or by a rebound.
Run toward the basket, but stay either to the left or right of the basket. This way you'll be able to see what your teammates are doing as they approach the basket. Look for a teammate that is running down the lane straight at the basket.
Press and hold the "L2" button, then press "X" just as your teammate is running toward the basket and they'll perform an alley oop. They should be in the lane and roughly halfway towards the basket when you pass it.