Can an adult get in trouble for picking a fight with a minor? Does the minor have to testify against the adult, or can a videotape of the incident be used as evidence?
Depending on the exact situation, most states do not have laws that punish adults for fighting with minors. A person may incur criminal charges if he or she assaults and/or batters any person regardless of age. If this occurs, the minor or the police can press charges against the adult. Similarly, if an adult attacks another adult, then the victim or the police can press charges as well.
In regard to your second question, the minor may testify against the adult in court, and the videotape may be shown as evidence. Additionally, if other people witnessed the incident, they may be allowed to testify as well.
You should consult with a local criminal defense attorney for legal advice pertaining to assault and battery within your state.