Understanding the NFL Rulebook

The NFL rulebook is a compendium of the official NFL rules. Issued each year by the NFL Rules committee, it changes from season to season to ensure fairness and player safety. 

Most of the rules are very straightforward. For example, an NFL season consists of 16 regular-season games and the field must be 360 feet long and 160 feet wide, with 30-foot end zones on either side. The crossbar on the goalpost must be 10 feet off the ground, and the posts must be 18 feet and 6 inches apart from each other.

Common Rules
It's easy to enjoy a football game if you know the basic rules, which include the following:

• False Start: No member of the team that has posession of the ball can move before the ball is snapped by the center. If an offensive player flinches and draws the defending team to move, this is penalized as inducement.
• Encroachment: No member of the defending team can move across the line of scrimmage and make contact with an opponent before the ball is snapped by the center of the team with the ball. The defenders at the front of the line also cannot move before the ball is snapped if they take a three-point stance, supporting the body with their legs and one hand on the field.
• Neutral Zone Infraction: This is similar to encroachment, but the defensive player doesn't make contact with an opponent, he simply gets his opponent to move. An offsides penalty is called if a defender lines up too close to the opposing team before the snap.
• Intentional Grounding: As long as the quarterback remains in the pocket behind his defenders, he must attempt to throw a pass to a player who can make the catch or fall to the ground with the ball if defenders are about to sack him. Once the quarterback moves out of the pocket, he can throw the ball to the ground or out of bounds to avoid a sack.
• Pass Interference: When the ball is in the air, any player able to catch it has the right to do so. Players cannot tackle a receiver before he can get the ball, pull him down or grab his arms or hands to prevent him from getting the ball. This rule applies to both the team with the ball and the defenders; offensive pass interference is called if a wide receiver prevents a defender from making an interception by grabbing his hands or tackling him before he can catch the ball. This is one of the most severe penalties in the game, as the ball is placed at the place where the penalty occurred.
• Out of Bounds: When a player catches the ball, both of his feet must touch the ground before he goes out of bounds on the sidelines. This rule was changed before the 2008 season so that a player who is pushed out of bounds while in the air is considered out of bounds. In previous years, a force out was considered an in-bounds catch if the official determined that the player would have landed in bounds without the push.

Player Safety Rules
Certain rules exist to prevent players from severe injury. These dictate how and when a player can be tackled.

• Face Mask: No player can grab another player's face mask and use it to tackle him or bring him to the ground. This is the most severe regular penalty in the game, resulting in a 15-yard penalty for the offending team.
• Late Hit: Once play has stopped on the field, either by the referee blowing his whistle to end it or by a player going out of bounds, players cannot be tackled or hit.
• Unneccesary Roughness: This can be called if a player uses an illegal tackle, such as a horse-collar where a player is brought down from behind by his shoulder pads, or if a group of players uses excessive force in tackling an opponent.
• Chop Blocks/Tripping: In most circumstances, players are not allowed to tackle below the knees. A chop block occurs when two players tackle an opponent, with one going high and the other hitting low. Tripping can be called when a player on the ground reaches out with his feet or hands to bring down an opponent who does not have posession of the ball.
• Special Rules for Quarterbacks: Quarterbacks cannot be hit by defenders once the ball has traveled 15 yards from their hands. Defenders with a clear path to the quarterback cannot tackle them below the knees. If a quarterback is held by multiple defenders and is still attempting to complete a play, the officials can choose to whistle the play dead to protect the quarterback. These penalties are enforced as roughing the passer penalties.
• Special Rules for Kickers: On field goals, punts and point after tries, a kicker cannot be hit while his leg is in the fully extended kicking position.

Rules for Fumbles
Fumbles are a constant source of argument among football fans, and few fumbles go unchallenged in this era of the instant replay.

• Safety: A safety is usually scored when an offensive player is tackled in his own end zone, but there are also two ways that a fumble can become a safety. If a punt is blocked by the punting team and rolls out of the end zone, it will be scored as a safety. The receiving team in a punt will be charged with a safety if the receiver fumbles the ball out of his own end zone or if the kicking team recovers a fumble in the receiving team's end zone.
• Forward Pass: One of the most controversial rules in the NFL is the rule that governs quarterback fumbles. If the ball is knocked from a QB's hand as it is moving forward to make a pass, the play is ruled an incomplete forward pass rather than a fumble. It's up to the officials to determine whether the hand was moving forward, and in any situation half the fans watching will dispute the call.
• Ground Interference: If a player has posession of the football and loses it as he's tackled, it's not considered a fumble. For this rule to apply, a player generally must have both knees or one elbow on the ground.
• Recovering Fumbles: During the last two minutes of each half and on any fourth-down play, the offensive player who fumbles is the only member of the offense who can recover a fumble. Any member of the defensive team can recover a fumble in these situations, but if another offensive player touches the loose ball, the play is whistled dead at the spot of the fumble.