Instructions
Take a shot that fails to sink, either accidentally or purposefully, with the "Square" "B" or "X" button. This is easier to do if you shoot a two pointer too early, as the goal is to take a shot that swirls around or bounces off the rim.
Advance toward the hoop with the same player that took the failed shot while holding down two turbo buttons, which is easiest to do with both the "L" and "R" buttons.
Press "Y" or "Triangle" while holding both turbo buttons to jump at the ball as it's rebounding. If the timing is correct, you will execute the Put Back Dunk, which is a level 2 dunk.