Why did Rihanna and chris brown get in a fight?

Because Rihanna slept with J-Z and got a desease from him and then passed it to Chris Brown when they slept together

Another thing that people think happened was that Rihanna found out that Chris Brown was cheating on her when she saw is txt's, so she threw his phone out the window. Chris lost his temper, stopped the car, got out, picked up a large rock, and smashed her face with it.