An assistant referee, commonly known as a linesman, is a key member of the officiating team in sports like soccer, rugby, and field hockey. In American football, an assistant referee is referred to as a side judge. Other synonyms for assistant referee include assistant umpire, assistant official, sideline judge, and touch judge. However, these terms may vary depending on the sport, level of competition, and governing body. Regardless of the title they hold, assistant referees play a vital role in helping the head referee make accurate and fair decisions on the field of play. Their job is to observe and signal any violations or infractions that the referee may not be able to see from his position.