The main function of a goalkeeper in football (soccer) is to prevent the opposing team from scoring by saving shots on goal. Goalkeepers play a critical role in the team's defense, using their agility, reflexes, and decision-making skills to react to incoming shots and crosses. They are the only players allowed to use their hands within the penalty area, which gives them a unique advantage. Good communication with defenders and an understanding of the game are essential for a goalkeeper to effectively organize the defensive unit and contribute to the team's overall performance.