Saw something very similar happen 2 weekends ago. Parents from other team sitting on wrong side started bad-mouthing players from our team. They were verbally abusing one in particular, who is a extremely talented and aggressive player, and the nearby-sitting Mom had enough at one point and yelled to them that her DD wasn't fouling she was just dribbling the ball. That started a series of back-and-forth shouting which finally died down. At which point a different Mom from our team quietly suggested that if they wanted to bad-mouth the 12 and 13-year old girls on our team, they should probably go sit on their own side. One of the other team (male) parents took extreme offense at being asked to move, and got up into the Mom's face in a very threatening manner, shouting and gesturing violently. Then a older brother from our team stood up to defend this Mom (not his own), and some near-shoving and people jumping in-between. Ugly, just plain ugly... It was interesting to me that nothing shouted upset this hothead parent until it was suggested in a calm, quiet voice they sit elsewhere, and then he blew a gasket and was foaming at the mouth.
It still blows my mind how many parents sit on the wrong side and then start in on heckling and bashing the children. And yes, we did win, and as you might expect, every goal we scored resulted in more and louder celebrating from our side than was usual. And still they sat there, looking like they were chewing on lemons.