NEWELL, Iowa — The streets of Newell and Fonda are quiet. Rural decline has taken a toll on these northwest Iowa towns with main street storefronts shuttered and vacant houses scattered here and there. Yet the heart of these communities separated by 9 miles isn’t hard to find. It still beats at the Newell-Fonda High School gym, where many of Newell’s 850 residents, Fonda’s 600 and folks from surrounding farms dress in blue and fill it up to cheer on their beloved girls basketball team that is known across Iowa. With 21 of the school’s 71 girls in grades 9-12 playing on the varsity or junior varsity teams, the Mustangs are an outlier. Participation in girls basketball...