Carl and I dig into the opportunity generated by the Covid-19 pandemic to study natural experiments in sports. Many of the things we used to take for granted--stadiums full of fans, weekly travel schedules, consistent training opportunities--have been disrupted for some or all players, in tennis and other major sports. We consider what we can learn about home-court advantage, the predictability of results, the role of unchanging venues, and even the speed of play, by comparing pre-pandemic numbers with their corresponding figures since sports got back underway. We also wonder about the limitations of these sorts of studies, because there are always confounding variables. The biggest confounder of all: the pandemic itself.