What triggers a legal snap in football?

A legal snap in football is initiated by the referee's signal indicating readiness. This signal ensures that all players are aware that the play is about to commence. The referee's role is crucial, as they confirm that both the offense and defense are set, and there are no penalties or infractions that would prevent the play from starting. The referee's authority in timing the snap helps maintain order and fairness in the game.

While other factors like crowd noise or defensive movement might influence a player's reaction or strategy, they do not constitute an official trigger for starting the play. Likewise, a quarterback’s call is important in terms of play direction but does not replace the necessity of the referee's signal as the definitive start of the snap. Facilitating a clear communication point with players is essential for the smooth execution of the game, which the referee's signal provides.