A long scar is a visible reminder of Scott Stone’s injury. Scott Stone doesn't remember the night he fell from the hands of a mosh-pit throng at a Seattle rock concert, but he bears its mark: a crescent-shaped scar that starts at his temple and disappears in his buzz-cut brown hair. Stone had gone to see an all-ages show by the California band Rage Against the Machine. Leaving his seat to join the fans packed in front of the stage, the then 14-year-old suddenly found himself hoisted up in the arms of strangers, being passed back, over the heads of...