My buddy was the Rec Department guy in a modestly sized town in Texas. He carried extra rule books, and when a parent was out of line or had overly-vocal complaints, he would calmly take them aside (he attended games every evening, at the big field area), tell them that he had teams with no coaches, perhaps the parent would like to take that team and their kid and start coaching? He'd hand them the book of rules while he was doing it. Same thing for people yelling at Umps, he'd take them to the side (everyone knew him), and tell them he had a chest protector and a counter, in just their size. He'd even offer them the little blue cap (he had them in his day pack). "No? Well, then, you can calm down or leave the sports complex, because that Ump can always forfeit your team due to your lack of sportsmanship." The town was small enough 20K that a cop was there every night, (some were coaches and a couple were umps), and were very willing to escort a loudmouth Karen to their vehicle. Or do a sobriety test (lots o' drinking in Texas).