We investigate the impact of the COVID-19 pandemic on the betting markets of professional and college sports. We find that during the pandemic, the moneyline betting markets of the National Basketball Association (NBA) became very inefficient. During this period, if one bet uniformly on underdog teams in the NBA, one could achieve a 16.7% profit margin. It is hypothesized that this inefficiency is due to the absence of live audiences during the NBA games. Such inefficiencies are not seen for any other sport. Much of the inefficiency comes from a small fraction of games with moneyline odds in the 233 to 400 range. We find that with clever strategies, one is able to achieve a 26-fold gain on an initial investment by betting on NBA underdogs during this time period.