They work in strange ways, the tennis fates. On the one hand, the 2021 U.S. Open stands proud as the Reset Major, the first big-time tennis event in 18 months to be played in front of a full crowd, a sign that we are progressing against COVID-19, back to full communal experiences. And yet the cast of characters will not feature Roger Federer, Rafa Nadal, Serena Williams, Venus Williams or Dominic Thiem, the defending champ and winner of the 2020 Ghost Open. This is like that dispiriting insert in your Broadway playbill announcing that Lin-Manuel Miranda and Kristin Chenoweth are under the weather and not appearing in tonight’s performance, replaced instead by understudies.