An offside offense occurs only if a player in an offside position becomes involved in active play by interfering with play, interfering with an opponent, or gaining an advantage.

The distinction between being 'in an offside position' and committing an 'offside offense' is crucial. A player only commits an offense if, while in an offside position, they actively participate in the game in one of three ways. 'Interfering with play' means playing or touching the ball passed or touched by a teammate. 'Interfering with an opponent' involves preventing an opponent from playing or being able to play the ball by obstructing the opponent's line of sight, challenging for the ball, or making a clear action that impacts an opponent's ability to play the ball. Lastly, 'gaining an advantage' covers situations where a player in an offside position plays the ball after it has rebounded or been deflected off a goalpost, crossbar, or an opponent, or after a save by an opponent. This ensures that a player cannot benefit from their illegal positioning even if the ball wasn't directly passed to them. The interpretation of 'gaining an advantage' and 'interfering with an opponent' often leads to the most contentious decisions, especially in high-stakes matches.