What indicates that the ball is in play on a free kick?

The correct answer identifies that the ball is considered in play when it is kicked and moves. According to the Laws of the Game, play officially starts on a free kick when the ball is physically in motion as a result of the kick. This means that a free kick must not only be taken, but the ball must also travel a distance, allowing players from both teams to engage with it.

When the referee blows the whistle, this indicates that the kick is to be taken; however, the ball is not yet in play at that moment. Similarly, defenders being set does not affect when the ball is considered in play; it is merely a procedural element before the kick is executed. Understanding the mechanics of a free kick is crucial for both referees and players to ensure that the game flows according to the established rules.