Not complaining, only commentaring
All NFL matches start with kickoff that is the ball is kept on the thirty yard line kicking tee of the team playing defense and a placekicker who is a special kicker in the team begins the game by kicking the ball to the team playing offensive. On the offense side of the team a kick return man tries to catch the ball and takes the game forward by running with it. At the point where the kick return man stops the drive of the offense begins in the rare cases when the kickoff ball ends in the end zone of the offense team the kick returner has two options – either run the ball beyond the end zone or kneel and signal touchback in the end zone itself. If the kick returner kneels the game is stopped and the ball placed at the 20 yard line for the offense team to begin play.
According to the NFL laws progress in the game of American football is measured in yards. Hence the team playing offensive has to gain maximum yardage possible by moving as close as possible to the end zone of the opponent team. Every time the ball ends up with the offense team they have 4 chances or downs to gain ten yards.