In short
The answer first
The Laws set the substitution framework, while each competition determines important details such as how many substitutes may be nominated and used within the permitted limits. A substitution follows a controlled procedure: the referee is informed, the outgoing player leaves, and the substitute enters only after receiving permission and at the appropriate point.
Key takeaways
Competition rules determine the permitted number of substitutes within the Laws' framework.
The referee must be informed before a substitution is made.
A substitute becomes a player when they enter the field in accordance with the procedure.
Competition rules may limit the number of substitution opportunities to reduce repeated stoppages.
Extra time, concussion protocols and youth or grassroots modifications can create competition-specific differences.
The Laws and the competition rules work together
Law 3 establishes the general framework for players and substitutes, but a league or tournament's regulations specify the operational number used in that competition. This is why substitution counts can differ between professional, youth, grassroots and certain tournament formats without contradicting the Laws.
When comparing matches from different competitions or eras, always check the relevant competition regulations instead of assuming one universal bench size or substitute limit.
The substitution procedure
The referee must be informed before a substitution. The player being replaced receives permission to leave and normally exits by the nearest boundary point unless directed otherwise. The substitute waits for the referee's signal and enters at the halfway line during a stoppage, subject to the procedure in Law 3.
Once the substitute enters correctly, the change is complete. The new player is now subject to all the same Laws and disciplinary consequences as any other player on the field.
Substitutes versus substitution opportunities
Many elite competitions distinguish the number of players a team may replace from the number of separate windows in which it may make those changes. Multiple replacements can be grouped into one opportunity, which helps limit tactical time-wasting and repeated interruptions.
Half-time changes and extra-time provisions may be treated differently depending on the competition. The match sheet and competition rules are therefore the best source for the exact allowance in a specific fixture.
Special protocols and modifications
IFAB permits or supports specific modifications and protocols in defined contexts, including additional permanent concussion substitutions and variations for certain levels of football. These should not be confused with an ordinary tactical substitution.
For fans, the safest interpretation is to separate the base Law from the tournament implementation. A broadcast saying a team has 'used all its windows' does not necessarily mean it has used the same number of individual substitutes.
Source check
Sources and further reading
KickVerse uses primary governing-body material where a rule or competition format has an official source. Analysis terms can vary between data providers, so provider-specific definitions are identified rather than presented as universal laws.
Continue learning
Related KickVerse guides that add useful context to this topic.