How should a referee signal a substitution?

A referee signals a substitution by holding up a substitution board because this method clearly communicates to the players, coaches, and spectators that a substitution is happening. The substitution board is a visual representation, often including numbers to indicate which player is coming off and which player is entering the match. This minimizes confusion and ensures that everyone understands the personnel changes on the field.

Using a loud whistle, waving an arm, or flashing a card are not standard procedures for signaling substitutions. A loud whistle is generally reserved for stopping play or getting attention, while waving an arm may not provide enough clarity regarding the substitution process. Flashing a card is used for disciplinary actions, such as showing a yellow or red card, and does not convey the intent of a substitution. Therefore, the use of a substitution board is the most effective and recognized method for this situation.