There are a bunch of crazy rumours attached to this story. One is that Brown assaulted Rihanna with an umbrella-ella-ella, another is that he hurt her because she gave him an STD (you know which one), and another that Brown flew into a rage after Rihanna accused him of cheating on her.
According to witnesses Princess RiRi and Chris Brown were arguing in their car when Brown hit her. By the time the police arrived, Brown had fled the scene (like a real man), but he eventually turned himself into the po-po and was released on $50 thousand bail.
Rihanna was treated at Ceders-Sinai (PS. Is there any other hospital in Hollywood? At all?) where she was apparently yelling and crying. Understandable. According to TMZ, Rihanna had bite marks and bruises all over her body.
This is very not good. Fuck you, Chris Brown. Nobody does that to another person, especially not one they love, especially not one who brought us 'Umbrella'.