LAHTI, Finland — A collective gasp fell through the stands. Flags bearing Norway’s iconic red, blue and white symbol, previously waving, went limp. With half a kilometer left in the men’s 30 k skiathlon at the 2017 Nordic World Championships in Lahti, Norway’s race favorite Martin Johnsrud Sundby had fallen. A half a second earlier on Saturday, the Norwegian’s shot at the win was still within sight. He and Russia’s Sergey Ustiugov had broken away from the...