If you dont like kickball, put in a 3 line rule like indoor. Or copy hockey's icing rule.Then the game will be as crappy and slow as American football. Nor does that resolve the endurance problem. Rotating girls in and out provides recovery time that leads to press and kickball soccer. NC has perfected it; it's ugly and ruins the game. And there is no evidence that coaches take out kids more for injuries when they have unlimited substitutions - none.