https://www.gamespot.com/articles/nba-2k18-pre-load-now-available/1100-6453291/

Ahead of NBA 2K18's official release, people who pre-ordered the professional basketball game can pre-load it right now on PlayStation 4 and Xbox One. Pre-loading lets you install the game to your system so you can play the moment it officially unlocks.

People who pre-order get the Early Tip-Off Edition, which unlocks on September 15, ahead of the game's official release date on September 19.