Well, it was sexual assault. not rape. assault could be nothing more than verbal in nature, i think.
So in my mind what happened is this chick was serving him at the resort or whatever and was hitting on him and he pushed her off or made fun of her.
She gets mad, tells the cops. The cops went and asked a judge to authorise an arrest warrant because 'they thought there was enough evidence'. So he gets arrested before any charges are actually made.
Now, its up to the DA to make any formal charges, and i bet he doesn't because its just one 19 year old biotch that got mad cause she didn't get 'treated well' by a multi milionaire NBA star.