The term "behind closed doors" is used in several sports to describe matches played where spectators are not allowed in the stadium or venue to watch. A match played in this manner is also referred to as a crowdless game. Because ticket sales generally constitute a substantial proportion of total revenues in most professional sports as well as in certain elite competitions of many amateur sports, it is rare for such games to be off limits to paying members of the general public. When such instances do occur, it is usually for reasons outside the participating teams' control. These may include as a punishment or remedy for a participating team, stadium safety problems, preventing potentially dangerous clashes between rival supporters, wider safety concerns, or public health concerns like the COVID-19 pandemic.