Parents usually play a vital role in the success of their children in chess as well as in other sports. Parents can give their children important emotional and mental support. Parents should be the #1 role model for their children. It is such a big plus having loving and supporting parents.
However, a small percentage of parents sometimes do go overboard. I have personally witnessed on a number of occasions where parents clearly crossed the line at various chess events. Some are loud, rude and some even get physical or violent. Some behave worst than their kids. Once that line is crossed, things are no longer “fun” for their children and they lose interest in chess or in other sports.
A few days ago, a case in youth football made the national headlines. After the son of an assistant coach was hit (late) after a play was over, the assistant coach charged the field and assaulted the kid who made the late play on his son. Yes, the other boy clearly made an illegal play. But that is why you have referees / TDs to handle matters like this in sports or in chess. If you feel that the referees / TDs are not doing their jobs, you can file formal complaints against the referees / TDs or the other party.
However, parents should NEVER take matters into their own hands by getting physical or violent, especially against another child.
Here is the video. Be your own judge!