Yes, you should speak with a criminal defense attorney.  As is usual, you and the others were "grouped" together to file the charges against and you may in fact be held responsible under the law, depending on the facts and circumstances surrounding the injury to the police officer.  This could be a very serious charge to you and you need behind you someone who knows how to help you stand out from the crowd, so to speak, and differentiate what happened to your benefit, if possible.  You are 20, not a child anymore.  You will be charged and sentenced as an adult.  Start thinking about consequences when you act.  Good luck.