If a player is injured, when should the official start the 20-second substitution timer?

The 20-second substitution timer should be started after the injured player has left the court. This timing is crucial because it allows for an accurate assessment of the situation and ensures that the substitution is made efficiently without disrupting the flow of the game. Once the player is off the court, the official can count down the 20 seconds to provide the team with an opportunity to send in a substitute. Starting the timer before the player has exited the court may lead to confusion and could potentially hinder the player's ability to receive necessary medical attention or cause unnecessary delays in game play. Thus, waiting until the player has completely left the court is the correct protocol according to the rules governing basketball.