Actually, the likeness rules give way to first amendment rights as to acts filmed in public. There are a few court cases saying that a state could not make it a crime to photograph and display an "upskirt" photograph, taken without the subject's consent. What happens in public is liable to be filmed by others and is fair game because of a lessened expectation of privacy. This is so even if the girls fighting are not adults. So the mere fact that one's likeness is involved, or a fighter is under age, is not determinative. What I can say is that YT probably has a contractual provision that provides that it owns some intellectual interest in anything that was posted and displayed on its website. If YT objects, you will likely want to avoid confronting them.
You are, however, unlikely to encounter any resistance on such posting. If you do, you can always choose to take it down. The danger involved in the NON-COMMERCIAL display of materials is small. The likeness statutes normally make one disgorge profits from unauthorized use, and there are no profits in non-commercial displays. You could consider putting a "Fair Use" copyright disclaimer on everything you post. You are educating the public.
