The National Football League is the pinnacle of competition worldwide. The NFL has the best players and rules that dictate how the game is played, scored and penalties are administered. Here is an overview of the NFL rules.

The NFL field is a rectangle that is a total of 120-yards long. The middle 100-yards are divided into sections 5-yards long, and lined from sideline to sideline. At either end there is a 10-yard area called the end zone.

The entire field is bordered by a 6-foot thick out-of-bounds line. At each end, there is a goal line marking where the 10-yard end zone begins. There are numbers marking the 10, 20, 30, and 40 yard lines up to the middle of the field, or 50-yard line.

At the back of each end zone are goal posts. Each goal post has a bar parallel with and 10-feet off the ground. There are two upright posts that are 18½-feet wide and extend vertically 30-feet high.

The time parameters in an NFL game are the easiest of the rules to understand. Time in an NFL game is regulated by quarters, a game clock and a play clock.

Quarters – An NFL football game is divided into four quarters. Between the second and third quarter, there is an extended break period called halftime. Halftime is 12-minutes long in professional football.

Game Clock - Each of the four quarters are 15-minutes long. Most play is under a running clock. When there is a penalty or a player goes out of bounds, specific rules dictate the clock starts when the ball is snapped. Here is a list of situations when officials temporally stop the game clock according to NFL rules.

• Each time a runner is forced out of bounds
   
• When passes are incomplete
   
• During the time period when teams change possession
   
• For all timeouts, including injuries
   
• After each and during the administration of penalties
   
• After every scoring play
   
• First down measurements by the officiating crew
   
• At the two-minute point before halftime and at the end of the game
   
• After each quarter gun sounds
   

Play Clock – NFL rules stipulate that there is only so much time between the end of one play and the point when the offense must start the next play. This is the play clock. The standard play clock is 40-seconds after the previous play is over. After quarters, timeouts and penalties, the play clock is set at 25-seconds. A violation is called a delay of game and is penalized by moving the ball back 5-yards.

Each NFL game is regulated by a series of rules for game play. The design of these rules is what dictated various strategies. Here is a basic outline of game play according to the NFL rules.

Players – Each team is permitted to have 11 players on the field during a play. There are specific rules that govern substitution between plays, but never can there be more than 11 offensive and defensive players on the field at one time. A violation is a yardage lost penalty.

The Kick Off – Each game and subsequent half start with a kickoff. The kick off is from the 35-yard line on the kicking team's side of the ball. After every score except a safety, the scoring team kicks off to the opposition.

Line of scrimmage – The ball is at a given point on the field for every play. This yard line is called the line of scrimmage. All players from the offense and defense must remain on their own side of this line. Any player whose body is across this line, or who starts and crosses this line before the ball is snapped, is penalized for offsides.

Line to gain – Play is divided into 10-yard segments. There are markers indicating where the ball is at the beginning of the play, and marker 10-yards from the original spot.

Downs - Each offensive series is divided into four downs. The offense has four plays to pass the yard to gain line. After three attempts, they can choose to punt the ball away. If they try to reach the line to gain on a fourth play and fail, they surrender the ball to the opposition at that spot.

Moving the Ball – Offenses can move the ball two different ways. The can hand it off or lateral it to a running back. Players may also throw the ball forwards, as long as they are behind the line of scrimmage. Each player in possession of the football is considered a runner.

Runner Down – To stop the play, the defense must get the runner to the ground. As soon as a runner's knee or backside comes in contact the ground because of an act by a defender, the player is down. In the NFL, runners who fall down untouched can get back up and resume running.

Mark the Ball – At each point a runner is ruled down by contact, this is the spot on the field the officials will mark the ball. A new play will begin according to rule.

Blocking vs. Holding – To open space for runners' teammates may screen and block the opponents. Players cannot grab or hook defenders to stop them from pursuing the ball carrier. This is holding and is penalized 10-yards from the spot of the hold. Neither offensive nor defensive players are permitted to put their hands into the facemask of the opponent. This is a facemask penalty for grabbing, or hands to the face for other infractions.

There are additional penalties that officials call to regulate each NFL game. Many of rules are designed to enhance player safety in an otherwise violent sport.

• Targeting – Players cannot lead with their helmet, contacting an opponent's helmet with the initial contact. This is targeting and is considered an unsportsmanlike foul.
   
• Pass Interference – Defenders cannot hold or impede a player's attempt to catch a forward pass. The rules for these two infractions vary. Holding is yardage penalty and a new set of downs, while interference is spot-of-the-foul infraction.
   
• Illegal Motion – There are rules that dictate how many offensive players can be in motion legally prior to the snap of the ball. A violation is a 5-yard penalty against the offense.
   

There are other rules covering blocking and tackling situations, but many of those are rarely called, and are specific to game situations. Blocking in the back and tripping are two of these. The three penalties detailed above are the most frequently flagged violations, according to NFL rules.

Under NFL rules, there are four ways to score points. One way can be accomplished by both the offense and the defense. The other two methods are more specific. Only the defense can score a safety and only the offense can kick a field goal. Here are the ways teams score points in an NFL football game.

• Touchdown (6-points) – TDs as they are called, can be scored by either the offense or the defense. Defenders may intercept a forward pass or pick up a fumble. The offense can run the ball across the goal line, or catch a pass in the end zone.
   
• Conversion (1 or 2-points) – After each touchdown, the offense will attempt what is called a conversion, or try. If they choose to kick the ball, they are awarded one additional point. Teams can elect to attempt to run or pass the ball into the end zone and be awarded a 2-point conversion.
   
• Field Goals (3-points) – At any point during their possession, the offense may elect to kick a field goal. The ball must clear the 10-foot cross bar, between the uprights to be successful.
   
• Safety (2-points) – The defense can also score points by tackling the opposition ball carrier behind their own goal line. This is a safety. After a safety, the team tackled must surrender the ball via a free kick to the team that scored. This is the only time in American football rules where the team scoring points receives the ball.