Football Field
The football field is 120 yards long and 53 ½ yards wide. At each end of the field and 100 yards apart are the goal lines. The additional 10 yards at each end is the end zone. The field is divided up every 5 yards by a yard line. The middle yard line marker is called the 50 yard line. In parallel to the side lines are rows of hash marks. The football is always placed on or between the hash marks at the start of each play. This ensures that the teams have space to line up on both sides of the football. The position of the football that defines the sides of the ball is called the "line of scrimmage".
There are also goal posts at the back of each football end zone. One way to score is to kick the football through the goal posts. The ball must go between the uprights and over the crossbar.
If any part of a player with the football touches outside the side lines or the end zone it is considered Out of Bounds.
Game Format
Football is a timed sport. The team with the most points at the end of the time period, wins the game. The game is divided up into 4 periods or quarters with a long "half time" between the second and third quarter. Time is counted while plays are running and sometimes between plays (i.e. time continues after a running play where the player was tackled in bounds, but stops on an incomplete pass). To keep the game going at a good pace the offense has a limited time (called the play clock) between plays.
Football Players
The rules in football allow each team to have eleven players on the field at a time. Teams may substitute players between plays with no restrictions. Each team must start a play on their side of the ball.
The defensive players may take any position they want and can move about their side of the football prior to the play without restriction. Although there are certain defensive positions that have become common over time, there are no specific rules defining defensive positions or roles.
The offensive players, however, have several rules that define their position and what role they may take in the offense. Seven offensive players must be lined up on the line of scrimmage. The other four players must be lined up at least one yard behind the line of scrimmage. All of the offensive football players must be set, or still, prior to the play beginning with the exception of one of the four backs which may be moving parallel or away from the line of scrimmage. Further rules say that only the four backs and the players at each end of the line of scrimmage may catch a pass or run the football.
The Football Play
The team with the possession of the football is called the offense. The offense tries to advance the football on plays. The defense tries to prevent the offense from scoring or advancing the football. The down system: The offense must advance the ball at least 10 yards every four plays or downs. Each time the offense is successful in advancing the ball 10 yards, they get four more downs or what is called a "first down". If the offense does not get 10 yards in four plays, the other team gains possession of the football at the current line of scrimmage. In order to keep the other team from getting good field position the offense can punt (kick) the ball to the other team intentionally. This is often done on 4th down, when the offense is outside of field goal range. Offensive plays on downs start with a snap. This is when the center passes the football between their legs to one of the offensive backs (usually the quarterback). The ball is advanced either by running with the football (called rushing) or passing the football. The football play is over when 1) the player with the football is tackled or goes out of bounds 2) an incomplete pass 3) there is a score.
The offensive team can lose possession of the football by:
Scoring
Not getting 10 yards in four downs.
Fumbling or dropping the football and the defensive team recovers it.
Throwing the football to a defensive player for an interception.
Punting or kicking the football to the defensive team.
Missing a field goal.
Getting tackled in the end zone for a safety.
Football Penalties
There are many rules and penalties that are enforced during a football game. Most football penalties result in a loss or gain of yardage depending on whether the penalty is against the offense or the defense. The severity of the penalty determines the number of yards. Most penalties are 5 or 10 yards, but some personal foul penalties result in 15 yards. Also, pass interference can result in a penalty that matches the length of the intended pass. The team that did not commit the penalty has the right to decline the penalty. We won't list or detail every possible football infraction, but here are some of the more common football penalties:
False Start: When a football player on the offense moves just prior to the snap. This is a five yard penalty. Note that one back on the offense can legally be "in motion" at the time of the snap.
Offside: If a player from the offense or defense is on the wrong side of the line of scrimmage at the time of the snap. A defensive player can cross the line of scrimmage as long as they get back before the snap, but if they touch an offensive player they can be called for encroachment.
Holding: When a player grabs a football player without the ball with the hands or hooks him or tackles him.
Pass Interference: When a defender contacts a pass receiver after the ball is in the air to prevent him from catching the ball. This is up to the referee to determine. If the contact is before the ball is in the air it will be called defensive holding. Note that pass interference can also be called on the offense if the defender has position and is trying to catch the ball.
Facemask: To protect the football players, it is illegal to grab another player's facemask.
Roughing the Passer or Kicker: To protect kickers and quarterbacks, who are very vulnerable when they are passing or kicking the ball, players are not allowed to run into them after the ball has been thrown or kicked.
Intentional Grounding: When the passer throws a pass nowhere near an eligible receiver strictly to avoid being sacked.
Ineligible Receiver Downfield: When one of the offensive players that is not an eligible receiver is more than 5 yards downfield from the line of scrimmage during a forward pass.
Field and equipment