Substitutions in Under-19 and Under-16 games may occur with the referee’s permission as follows:
By either team...
By the team in possession of the ball...
By the team not in possession of the ball, if the team in possession of the ball is substituting...
Coaches may substitute a cautioned player at their discretion and only at the time the player is cautioned.
Referees and coaches should remember that unnecessary delays should be prevented. This includes a request for substitution just as a ball is being put into play. This often may result in the ball being called back and the restart retaken. It also includes times when the substitute player is not ready to take the field when the request for substitution is made. In these cases the referee should allow the restart to continue and inform the coach that the substitution can occur at the next stoppage. Players should indicate to the referee that they wish to substitute by being at the halfway line before the stopage.
Referees should not deny requests for substitution even if the purpose appears to be wasting of time. The referee, though, should add time lost from such requests.