A new superstar appeared on the American sports landscape in the spring of 2006: Barbaro, a three-year-old racehorse, won the Kentucky Derby by six and a half lengths, the largest margin of victory in sixty years. Barbaro's impressive performance immediately stirred talk of a possible Triple Crown. But in the opening yards of the Preakness Stakes two weeks later, the horse suffered a catastrophic leg injury that ended his undefeated career and left...