The last, and arguably most crucial innovation, which would eventually make American football uniquely "American", was the legalization of interference, or blocking, a tactic which was highly unlawful underneath the rugby-design procedures. Interference remains strictly unlawful in both rugby codes. The prohibition of interference inside the rugby activity stems from the game's rigorous enforcement of its offside rule, which prohibited any participant within the staff with possession from the ball to loiter amongst the ball and the aim. At the outset, American players would locate Artistic ways of aiding the runner by pretending to accidentally knock into defenders looking to deal with the runner.
A modern down indicator box is mounted on a pole and it is used to mark site the current line of scrimmage. The number around the marker is changed using a dial. Officers are responsible for implementing activity regulations and checking the clock. All officers carry a whistle and put on black-and-white striped shirts and black hats except for the referee, whose hat is white. Each carries a weighted yellow flag that is thrown to the bottom to sign that a foul has become named.