It is probably legal. All police need to issue a citation or make an arrest is something called probable cause
. Probable cause is simply a reasonable belief that a crime may have been committed and that a particular person, in this case, your son, may have committed it. It takes very little evidence, and the word of a credible eyewitness that your son kicked the car in the parking lot can be enough to provide it.
Now, once the case goes to court, the state eventually needs to prove that he did this beyond a reasonable doubt. That takea s great deal of evidence, and if hte state fails your son must get acquitted. So what I'm trying to say is that it's easy to get charged with a crime but far more difficult to get convicted of it.
He was not detained because the charge is non-violent
and he almost certainly has had no trouble with the law before. It's pretty typical that under these circumstances a person will get a citation or a summons and be trusted to come back to court
He will need a lawyer, and he should get one as quickly as he possibly can. Certainly he should have one at his first court date if he could manage it. But even before that, someone (not him but a lawyer and/or his investigator) should try to make arrangements to inspect the car and to look for other witnesses in the bar before too much time passes.
Worst case scenario for something like this on a first arrest would be misdemeanor
probation and repayment for any damage to the car, the amount of which the state would have to verify, but he can likely get a more favorable disposition, even come out of this without a criminal record
, with counsel.