What should the official do when Player A1 kicks the ball backward to Player A2 during a kickoff?

During a kickoff, the Laws of the Game allow a player to kick the ball in any direction, including backward. When Player A1 initiates the kickoff and kicks the ball backward to Player A2, the play is deemed legal as the kickoff is designed to allow the team to transition the ball into play. The key factor is that the ball must move forward from the spot of the kickoff, and as long as it is touched and played correctly, which includes backward passes, the referee should allow play to continue. This aligns with the fundamental rules governing kickoffs, where the focus is on ensuring that the ball is put into play without restrictions on the direction of the first touch by the player.