The referees wear the black wristbands on their hands to keep track of the downs. There is a strap with a loop, and they move the loop to the next finger at the start of each new down. The free safety is free to move around to wherever he is needed. Both the free and strong safeties will play deep in a two-deep zone, and will split the field in half, which is called zone coverage. They will help out the cornerbacks and cover the sides of the field.
Safeties are usually bigger and better tacklers than the cornerbacks.
In the NFL, the defensive team cannot earn any points on a 2-point conversion. The ball is dead. Points For and Points Against. If a players hands the ball to someone in the stands, there is no fine. Some guys say that they get the ball back if the kick was wide right or left.