Down! Set! Hut! Football Quiz

The football is an oblong sphere and is 11 to 11.5 inches (28 to 29 centimeters) long. It has a lengthwise circumference of about 28.5 inches (72.4 centimeters) and a widthwise circumference of about 21.5 inches (54.6 centimeters) in the middle of the ball.

An NFL roster allows for no more than 53 players on a team. At any one time, only 11 players per team are allowed on the field.

A nose tackle is part of the defensive line.

A player cannot remove his helmet on the field unless it is to adjust his equipment. This rule is dubbed the "Emmitt Smith rule" because Smith, who holds the record for most rushing touchdowns, was famous for ripping off his helmet to celebrate a touchdown.

Twelve new footballs, sealed in a special box and shipped by the manufacturer, will be opened in the officials' locker room two hours prior to the starting time of the game. These balls are to be specially marked with the letter "K" and used exclusively for the kicking game.

As the angle of the kick gets steeper, the ball hangs in the air longer and goes higher. Also, as the angle of the kick is increased, the distance traveled by the ball increases to a maximum (achieved at 45 degrees) and then decreases.

When a player plants his foot to change directions, he applies force to the turf. The force that he applies to the turf helps him stop his previous motion and accelerate in the new direction.

Modern fantasy football can be traced back to the late Wilfred "Bill" Winkenbach, an Oakland area businessman and a limited partner in the Oakland Raiders.

In a salary cap game, the player acts as a virtual owner with a virtual bank account to draft players whose weekly game performances translate into points. In pick 'em leagues, the player picks who he or she believes will win between the two opposing teams in each of the NFL's weekly regular season contests. The managers' league is not a type of fantasy football league -- though it sounds good.

There are three popular positions on special teams: punter, placekicker and returner.

Goalposts extend 10 feet (3 meters) high.

Teams can stop the clock by running out of bounds, calling a time-out, or throwing an incomplete pass. Time stops for each half's two-minute warning as well.

When the opposing team drops the ball or if the defensive team intercepts the ball, it is called a turnover.

Each team is allotted two challenges per game. If the team loses the challenge, the team also loses a time-out.

Receivers run down the field and catch balls thrown by the quarterback. Depending on the field position, the receiver could either be a wide receiver or a tight end.

Once a player signals for a fair catch, he can't be tackled and can't move beyond the spot where he catches the ball.

When a play is challenged, the referee has 90 seconds to review the play at a field-level monitor on the side of the field.

If the ball holder is tackled behind the line of scrimmage, the team loses yards.

Gridcord is cotton thread covered with vinyl. It is used to lace the football.