Football Side Judge
The side judge in football is an official that is behind the defensive secondary and observes the playing field from behind. Their job is to make foul calls in the secondary and make decisions relating to their nearest sideline if needed, like if the player has stepped out of bounds.
The side judge is similar to a sideline referee in soccer, who runs up and down the sideline and signals when there is an offside situation. The side judge is positioned on the same side of the field as the head linesman. Their eyes are mainly on the defensive line, receivers and running backs. They'll keep tabs on the wide receiver to make sure that the defense doesn't interfere with his running route.
The side judge is required to observe and make calls for pass interference, illegal blocks, and incomplete passes. They are also required to keep count of the players to make sure there aren't too many on the field at once. Side judges stand and monitor the field goal kick from behind the defensive line and assist the clock operator, too. If the time clock goes down for some reason, the side judge is responsible for keeping track of game time. Like other officials, they are equipped with a whistle.