If you’ve ever wondered how to pull off a 360 dunk in NBA 2K14 (and NBA 2K15), look no further! How you do it is press X (square for PS3 and PS4) like going up for a dunk, and then rotate the L stick clock-wise in a circular direction immediately after. To practice this dunk, make sure the dunker you are using has a 360 dunk package equipped. For a demonstration, see the video below (1:15 mark).
Via STG
Ive tried both it doesnt work