How do concussion substitutes work?

Additional permanent concussion substitutions are an option in the IFAB Laws (Law 3.2) that a competition may adopt. They apply only where the competition rules allow them; the NSL Handbook does not set them out itself. Where used, the IFAB protocol applies in full:

• Each team may use one concussion substitute per match, regardless of how many substitutes it has already used.
• It can be made immediately, after an on-field or off-field assessment, or later, including after a player has been assessed and returned.
• The referee or fourth official is told, ideally with a substitution card or form of a different colour.
• The player takes no further part, including in a penalty shoot-out, and should where possible be accompanied to the dressing room or a medical facility.
• The opposing team may then use one additional substitute for any reason, with an extra substitution opportunity.
• A concussion substitution does not use a normal substitution opportunity, unless a normal substitution is made at the same time. Once all normal opportunities are used, a concussion substitution cannot be used to make a normal one.