What does the fourth official do, and when is one used?

Duties (Law 6, 2026/27): the fourth official's assistance includes:

• supervising the substitution procedure
• checking a player's or substitute's equipment
• the re-entry of a player following a signal or approval from the referee
• supervising the replacement balls
• indicating the minimum additional time the referee intends to play at the end of each half (including extra time)
• informing the referee of irresponsible behaviour by any technical area occupant

The referee, assistant referees, fourth official, additional assistant referees and reserve assistant referee are the "on-field" match officials. A reserve assistant referee may replace an assistant referee, fourth official or additional assistant referee who cannot continue.

When one is used: fourth officials are appointed to certain competitions by Canada Soccer or a Member Association (provincial or territorial association), and the duties are set by the Laws and the competition rules. Law 6 says competition rules must state clearly who replaces a match official who cannot start or continue, including whether the fourth official or the senior assistant referee takes over if the referee cannot continue.

If there is a fourth official: the assistant referee does not need to go to the halfway line for substitutions, unless there are several substitutions at the same time, in which case the assistant referee moves to the halfway line to assist.

Sources: IFAB Laws of the Game 2026/27, Law 6 and Practical guidelines for match officials; Canada Soccer Rules and Regulations, Regulation 19.11 (https://canadasoccer.com/wp-content/uploads/2026/04/CS_2025_RR_FINAL_EN-1.pdf).