Artificial crowd noise is pre-recorded audio that simulates the live sounds of spectators, particularly during sporting events. Sports teams have used artificial crowd noise to simulate stadium sounds during practices to acclimate themselves to conditions they would face in actual games, and some have accused teams of using artificial crowd noise on top of in-person crowds to distract opposing teams. Regular use of such audio grew during the COVID-19 pandemic, which has required many sporting events to be played with no spectators due to restrictions on gatherings or use of facilities. This audio is usually mixed to correspond with in-game events. Uses Some American football teams, particularly within the NFL, have used white noise or artificial crowd noise during practices to acclimate players to stadium conditions of actual games. It may also be mixed with music played at a similar volume to make it harder to tune out the increased sound. There have been accusations on several occasions, including the Indianapolis Colts in 2007, that teams have intentionally sweetened their in-person attendance with artificial crowd noise in an effort to distract the visiting team (with the Colts, in particular, accused of doing so to make it harder for the New England Patriots to call their plays). In the case of the former, the NFL exonerated the Colts and ruled that this had not actually occurred. In May 2013 during a Zürich Derby football match, fans of both clubs protested against heightened security measures by not entering the stadium until 10 minutes after kickoff. Swiss broadcaster SRF added artificial crowd noise to its highlights of the match, and later apologized for having manipulated the footage. Events being played behind closed doors The COVID-19 pandemic prompted teams to play many sporting events behind closed doors with no spectators to maintain player safety and reduce large gatherings that can spread Coronavirus disease 2019 (COVID-19). Artificial crowd noise has often been used to preserve a degree of normalcy (via a suspension of disbelief), especially during events where a lack of crowd may be considered unusual to viewers and/or players. Audio used for this purpose is often compiled from stock of previous games (in some cases, originally compiled for use in a sports video game). The crowd noise may also include audio associated with the sport or home team, such as specific chants, and in the case of football in South Africa, the sounds of