Do you not find Americans in general go OTT about sport a lot of them time?
I suppose that sort of depends on the sport. Yes, there are always some parents that go ballistic on occasion. But at least where I live (rural California), it's not a big issue. I'm on the board of our local AYSO Region (youth soccer), and our biggest problem every year are parents for U10 girls. I'm generalizing, of course, but it sure seems that at that particular age group, every dad wishes their daughter was a son, and every mom thinks their daughter is Mia Hamm. U10 girls' parents are the MOST obnoxious, every year. I think it might be because that is the first age group where we enforce offside, we keep score, and wins and losses count toward a tangible goal (medals or tournament play at the end of the season). That higher level of competitiveness, and having something at stake can bring out the worst in a parent, it seems.
But, as their kids get older, the parents always mellow out. By high school, most behave quite well. In fact, most high school players are pretty embarrassed by the loud or ignorant yelling from parents. As a referee, I get the eye-roll along with "sorry about that, he's my dad, ref" from a teenager at least once or twice a season...haha.
Some other American sports actively encourage dissent, such as baseball. The image of a manager kicking dirt on the umpire, turning his hat backwards so he can stick his nose in the umpire's face as he screams, that's considered normal for a "good" manager to stand up for his team against those awful umpires. (see
This Video for example!) The reason my son quit Little League (American youth baseball) was that he hated the coaches who yelled all the time, at umpires, other parents, and even the kids (both on his own team, and the opposing team). We haven't been back, and we haven't regretted it a single moment.