This paper examines whether sports betting markets are semistrong-form efficient—i.e., whether new information is rapidly and completely incorporated into betting prices. We use the news of ghost matches in the top European football leagues due to the COVID-19 pandemic as the arrival of public information. Because spectators are absent in ghost games, the home field advantage is reduced, and we test whether this information is fully reflected in betting prices. Our results show that bookmakers systematically overestimate a home team’s winning probability during the first period of the ghost games, which suggests that betting markets are, at least temporally, not semistrong-form efficient. We exploit a betting strategy that yields a positive net payoff over more than one month.