During the games have you noticed the green dot on the back of the quarterback's helmet? What is that all about?
The green dot means that the helmet has a radio transmitter inside of it. In the NFL, quarterbacks wear helmets with a radio inside, so that the coaches can talk to the player on the field.
Only one player at a time is allowed on the field with the specially designed helmets, so the green dot helps the referees keep track of who is wearing it.
Now you know the mystery behind that little green dot!