The diagonal system of control is the system of positioning used by match officials (referees and assistant referees) in association football

Football (soccer)

Association football, more commonly known as football or soccer, is a sport played between two teams of eleven players with a spherical ball...

 (soccer). This allows the referee to officiate in a fluid motion without needing to turn his back to the play, stop, and then turn around sharply.

Description

The diagonal system of control (DSC) can best be described by outlining the basic duties of the three match officials:

First, the two assistant referees are instructed by the referee to each patrol half of a single touchline on opposite sides of the field. For example, on a field running north-south, one assistant referee (AR) would run on the eastern touchline from the north goal line to the halfway line, while the other assistant referee would run on the western touchline from the south goal line to the halfway line. In general, the assistant referees' duties would be to indicate (using their flags): when an offside offence has occurred in their half, when a ball has left the pitch, and if a foul has been executed out of the view of the referee (typically in their quadrant of the field). Generally, the ARs will position themselves in line with either the second to last opponent or the ball — whichever is closer to the goal line — in order to better judge offside infractions. However, the assistant referee will have specific positioning with respect to corner kick

Corner kick

A corner kick is a method of restarting play in a game of association football. It was first devised in Sheffield under the Sheffield Rules 1867...

s, penalty kicks, and throw-in

Throw-in

A throw-in is a method of restarting play in a game of Association football.-Procedure:The throw-in is taken from the point where the ball crossed the touch-line. The throw-in is taken by the opponents of the player who last touched the ball when it crossed the touch-line, either on the ground or...

s.

Quadrant 1	Quadrant 2
Referee	Assistant
Assistant	Referee
Quadrant 3	Quadrant 4

The referee patrols the length of the field in order to cover the ground not covered by his two assistants, generally running in a diagonal pattern from the southeast quadrant of the field towards the northwest quadrant; hence the term "diagonal system of control". Note that this pattern is not a specific route but a general guideline that should be modified to the style of play, nature of the game, the location of play at a given time, etc. In some cases the referee may even exit the field if it aids in his decision making ability. The main idea is that the referee and assistants using the DSC should be able to position themselves quickly and easily to observe the important aspects of play (offside, ball in or out of play, goal-scoring opportunities, challenges for the ball) from multiple angles with multiple sets of eyes.

Note that the description above refers to a left diagonal system of control, known as "running a left" or "standard diagonal". If, before the match, the center referee on this field decides to run from southwest to northeast, then the assistants must position themselves accordingly and the result will be a right diagonal system of control, otherwise referred to as "running a right" or "reverse diagonal".

In international matches the left-wing diagonal shown above has been universal since the 1960s. It is now predominant across the world although a minority of referees in England still run the opposite diagonal and a very small number switch diagonal at half-time. The latter approach was mandatory in the Football League

The Football League

The Football League, also known as the npower Football League for sponsorship reasons, is a league competition featuring professional association football clubs from England and Wales. Founded in 1888, it is the oldest such competition in world football...

 until 1974 but since officials have had the choice most have opted to stick with the same diagonal throughout a game.

Its implementation as a standard practice for referees is attributed to Sir Stanley Rous

Stanley Rous

Sir Stanley Ford Rous, CBE was the 6th President of FIFA, serving from 1961 to 1974. He also served as secretary of the Football Association from 1934 to 1962 and was an international referee.-Early Life:...

, former referee and President of FIFA

FIFA

The Fédération Internationale de Football Association , commonly known by the acronym FIFA , is the international governing body of :association football, futsal and beach football. Its headquarters are located in Zurich, Switzerland, and its president is Sepp Blatter, who is in his fourth...

from 1961 to 1974.