ANN ARBOR – The quality of refereeing at the World Cup had been a source of relief until June 18, when referee Koman Coulibaly of Mali disallowed a perfectly legitimate goal by the United States that would have given it an all-important win over Slovenia. Worse still, Coulibaly never had to account for his terrible decision, or explain it to anyone – not the players and coaches on the pitch, and not the public at large.