In international matches the use of an assistant referee shall be compulsory.
The assistant referee shall have the same powers as the main referee, apart from those mentioned under Law V (d). Furthermore, the first part of Law V (e) shall also apply to him: "He shall have discretionary powers to stop the game for any infringement of the Laws."
If the main referee and the assistant referee both signal a foul simultaneously and there is a discrepancy as to which team is to be awarded the advantage, the decision of the main referee shall be given priority (cf Decisions, Law V.). The main referee and the assistant referee have the right to impose a caution or an expulsion, but in the case of a discrepancy between them, the main referee's decision shall prevail (cf Decisions, Law V.).
The assistant referee shall also have the following duties:
The assistant referee shall be equipped with a whistle.