An official whose responsibilities include adjudicating offsides and out of bounds, as well as aiding the referee in other decisions. Also known as an assistant referee.
The linesman, also referred to as the assistant referee, is one of two officials charged with standing directly on either touchline.
They also make calls regarding who gets possession of the ball after it's gone out of bounds, and also are the people responsible for denoting an offsides situation. Linesmen will constantly be moving, lining up with the final non-goalie defender in each of their halves.