Linesman
What is Linesman?
An on-ice official in ice hockey, the linesmen earned their name for being stationed near the center line or one of the blue lines and calling out rule violations concerning these lines. The linesman is responsible for watching for infractions like offside or icing. The linesmen are responsible for conducting faceoffs during the game. Another responsibility of the linesmen is to break up fights and other altercations that occur during the game.
Sporting Charts explains Linesman
The NHL uses a "four-official system" which mandates four on-ice officials be present for a hockey game. Other leagues use the "three-official system" which uses a single referee and two linesmen. This is one of the most common officiating systems and is used in the AHL. These officials consist of two referees, designated by their orange armbands, and two linesmen. The linesmen are not allowed to call penalties in the NHL, but they can report them to the referees. Some hockey leagues outside the NHL allow linesmen to call penalties during the game without referring them first to the referee. While the linesmen conduct the faceoffs during the game, the referees are responsible for conducting the initial faceoff at the start of each period.