As an American in the biathlon, Tim Burke is used to being overlooked by the sport’s most passionate fans. His German and Norwegian rivals are celebrities in their home countries, where biathlon is broadcast live on television and races draw up to 30,000 spectators. In Germany, he is perhaps best known as the boyfriend of Andrea Henkel, a two-time Olympic gold medalist. So when Burke took first place in the World Cup standings last weekend — the first time an American has ever done so — his achievement stunned the sport’s mostly European fan base.