Breaking the law is most always a violation of probation. Your son may contact his probation officer. The probation officer will likely speak tot he state attorney and review the police report
from the assault or battery. Your more worried about the possibility of his probation being revoked than any sentence
he may face for the current crime, as it was a misdemeanor
thus far. Also did your on notify his probation officer of his arrest? This is usually a requirement that a person on probation notify the officer within 24 hours of an arrest, this also could be a violation of probation if he did not.
The probation officer may make a report to the judge who sentenced him to probation. Your son has a right to a hearing, the probation officer may make recommended sanction,
which could lead to imposition of a jail sentence. Your son would have a right to be heard at this hearing, and the state would have to show by a preponderance of the evidence that he committed the crime which constituted the violation. This is not proof beyond a reasonable doubt, it simply means the judge believes it is more likely than not that he committed the act, it would not be a conviction, but a violation of the courts
This does not mean he will go to jail for the full term, even if he is found to be in violation, in most cases the judge can impose less severe sanctions such as extended probation, or more restrictive probation, or order a short term of jail time, such as a month.
The crime for which he is on probation for is a factor also, obviously the more severe, the more likely the severity of the penalty will increase.
Hope I gave you some insight into the process. He will have a right to be heard in court before his probation is revoked and the state still has the burden of proof. Thanks, XXXXX XXXXX luck with the case.