Please Help My Teenage Boy

My 14-years-old son got a trouble in school today. He used a computer, which he was not supposed to use, another kid shout at him "No computer". My son poked that boy on face with the eraser end of a pencil while walking away from the computer back to seat. The boy grabbed my son and pushed my son away. The classroom teacher noticed that. That boy insisted to send my son to the principal's office. My son admitted the mistake he made and signed the assault report. The teacher called me and told me that they might call sheriff next Monday. My son said that boy called him names and pushed him several times before. I talked to my son and he regretted what he did today. What can I do to avoid calling police? For the worst, if they do call the police, what should I do? Thank you very much in advance.