I used to watch Roller Derby when I was a boy. The fastest skaters would race out ahead trying to lap the pack, and if they did, their teammates would work to pick off the opposing skaters with body slams and worse, so that the speedster could pass them and score a point. Pass four skaters, get four points. Meanwhile, if the opposing team’s speedsters were approaching to try scoring some points of their own, the lead skater on your team could pop his or her hands down crisply on their hips and thereby “call off the jam.” This would end that particular play,…