I remember talking with my son about this when he was playing HS soccer. A couple of the AAAA schools had student fans with reputations for going over the line, and it was sometimes directed at him. As a player he always thought it was funny, and sometimes motivational, but never personal so long as it came from the students. He actually liked it when opponents students tried to razz him, it meant he was playing well. He gave them points for original put downs, and ignored the common everyday cuss words as too being too easy. In general, he always enjoyed student fans no matter what was said since he knew they were just trying to get in his head.
As for parents who crossed the line, he claimed it was easy to pick out their kids on the field, as it was usually the kid who was either cringing so bad or so lacking in skill in the first place that they likely were a vunerable point of attack. He felt that obnoxious parents hurt their own team more than they distracted the opponent. So maybe the other parents who want to see their kids succeed should be the ones discouraging this behavior.
