Jim Brown is arguably the best all-around athlete ever. He was a track star, one of the nation’s finest lacrosse players, averaged 38 points per game on his high school basketball team, and broke NFL records as a running back for the Cleveland Browns. In 2002, The Sporting News named him the greatest football player of all time. He was pretty handy with a tennis racquet, too. And he liked to wager on his matches. At a Las Vegas tennis club in...