The police officer has facial injuries from the encounter, possibly (although this is unknown for sure at this time) a broken eye socket. CNN, however, has reported that he absolutely does not have a broken eye socket.
In other words, we don't actually know what happened. There clearly was a scuffle as witnesses have already stated that Brown went after the officer in his car and that a gunshot was fired inside the car. Witnesses have also stated that Brown rushed Wilson right before he was shot, contradicting Brown's friend who said that Brown put up his hands.
Yet another reason to wait until all the facts are in before you hold up your sign saying "Arrest Darren Wilson".