Sha’Carri Richardson won her first Olympic gold medal, but a US 4×100 metres women’s and men’s double failed to materialize yet again because the men messed up two baton exchanges to finish second last and then be disqualified as Canada stormed to gold. The women’s 100m silver medallist Richardson came from behind in the pouring rain at the Stade de France for victory in 41.78 seconds together with Twanisha Terry, 100m bronze medallist Melissa Jefferson and 200m winner Gabby Thomas on Friday. Britain got silver in 41.85, and Germany, who had been surprise leaders at the final exchange, earned …