Final answer:
To authorize a kick-off, the referee blows their whistle after ensuring both teams are ready. Players from both teams must be on their respective sides of the field, with opponents at least 9.15 meters from the ball, which should be placed on the center spot.
Step-by-step explanation:
To authorize a kick-off in a soccer match, the referee will typically blow their whistle. This is the universally recognized signal that tells the players they can begin or resume the game. The whistle sounds clear and distinct and is usually done after the referee checks that both teams are ready, with the correct number of players on the field and the ball is placed on the center spot of the field.
After the whistle, the team that has been designated to take the kick-off will kick the ball and play commences. It is essential for both teams to be on their respective sides of the field and all players, except the player taking the kick-off, to be in their half of the field. Moreover, opponents of the team taking the kick-off must be at least 9.15 meters from the ball until it is in play.