When in mid-flight, you need to have your arms up for balance and to protect yourself as you jump. You need to hold your arms up to try and pull yourself forward to create power on the ball.
Players must be careful if they are going up for a header with an opponent because flailing arms can lead to a foul being conceded if the referee deems that you have made sufficient contact with an opponent to blow the whistle.
When you are defending, you usually want to head the ball as high up in the air and as far away as possible. Leap up, body arched and back ready to give power to the neck.
