I Formation – An I Formation is an offensive formation where both of the backs line up directly behind the quarterback, making a formation that resembles an “I”. The back who is closest to the quarterback is called the fullback, and the other behind the fullback is called the running back, tailback or I-back. These two backs line up either in a line or with the fullback offset to either side. The formation may take the form of offset weakside or offset strongside. In either case, the fourth back is generally employed as an extra wide receiver. Other variations of the I formation include the Maryland I and the Power I. Both of these formations lack the flanker, using the three running backs rather than a standard two. The Maryland and Power I formations are used mostly for running and may employe either tight ends, split ends or one of each.

Illegal Formation – In the NFL and NCAA, an offensive formation in which less than seven players are lined up on the line of scrimmage is an illegal formation. Rules state that all formations must consist of left and right tackle and left and right guard, as well as a center. These players are responsible for blocking, and as a group are referred to as the line. There must also be two other players on the line of scrimmage, the Ends, who are eligible receivers. The formation also includes three other backs, who can be either halfbacks or fullbacks or they can act as extra tight ends or receivers. Additionally, the offense must set their formation before the play, meaning that the players must all be in position and motionless for at least one second before the ball is snapped. The defense, in contrast, does not have strict rules regarding formation and may line up anywhere on its side of the neutral zone.

Illegal Motion – Illegal Motion is a penalty that is called when two offensive players are in motion at the same time at the snap of the ball, or when a player moves towards the line of scrimmage prior to the snap. Illegal motion results in a five yard penalty against the offending team.A receiver or back is allowed to be in motion prior to the snap as long as he isn't moving towards the line of scrimmage. Rules state that only one offensive player is allowed to be in motion when setting up the play. The referee signal for an illegal motion penalty is putting one arm in front of the chest, with the palm open and down, with the elbow out to the side of the body, moved away from chest. Illegal motion differs from an illegal shift, which occurs if a player is not in motion, but is not set prior to the snap.

Illegal Procedure – See “False Start”

Illegal Shift – An illegal shift is a foul that is called when an offensive player hasn’t reset for at least one second before the ball is snapped after two or more players shift simultaneously. The penalty for an illegal shift is five yards against the offending team. Rules require that the offensive line is set for a full second before the snap. An illegal shift penalty is assessed for various reasons: because a player is in motion but not set prior to the snap, or when more than one player is in motion at the time of the snap, for example. After a player moves, all eleven players must be motionless for at least one second before the snap. The referee signal for an illegal shift violation is to move both arms in front of the chest, with palms open and down and elbows out to the side, moving arms away from the chest.

Inbounds – The area of a football field that falls between the sidelines and the endlines is considered to be inbounds. The total are of a football field is 360 by 160 feet. The longer boundary lines are the sidelines, and the shorter lines are sidelines. Both sidelines and endlines are out of bounds. Whenever either the ball itself or the ball carrier touches the sideline or endline or otherwise goes outside the field of play, the ball is a dead ball and ends the current down. When a receiver catches a pass, he must catch the ball with both feet established in bounds. When a fumble occurs and the ball goes out of bounds, possession is awarded to the last team to have legal possession of the ball. Although a receiver cannot go out of bounds and return to the legal playing field to make a catch, they can be out of bounds and return to the field to make a legal tackle.

Incomplete Pass – A pass which is thrown by the quarterback in a football game but which the intended receiver fails to catch. The incomplete pass is something that no football player wants to get. They especially do not want an incomplete during an important game such as the Super Bowl. An incompletion is a time where the football is launched to a receiver and then when the ball reaches him, it hits the ground just before being caught and put under control by the receiver. Also after an incomplete pass, the ball is spotted back to the previous line of scrimmage. Once an incomplete pass is made, it is moved back to the line of scrimmage and it causes the down to advance by one and additionally no yards are gained by the offensive side. Additionally, the game clock is stopped. There is also an intentional incomplete pass which is when the quarterback is about to get sacked and he throws the ball out of bounds to avoid any kind of loss of yards. Bottom line: The victim of the incomplete pass is caught off guard.

Incompletion – See also “Incomplete Pass.” An incompletion is how an incomplete pass is officially designated in the football records and books. It refers to an incident in which the quarterback has thrown the ball to a potential receiver without the receiver successfully holding onto it. As a result, the team loses that down and in some cases some yards. Following the incompletion, the referees spot the ball back to the previous line of scrimmage. This causes the down to advance by one and also causes the game clock to stop. While generally an incompletion is frowned upon, there can be times when it can be useful to the team. For instance, if a team is behind on the scoreboard and also lacking in time-outs, then near the end of the game, it's sometimes better for an incompletion to take place than for the quarterback to waste valuable seconds by looking and looking for an open receiver.

Intentional Grounding – A kind of penalty in football where the quarterback throws the football away to avoid being sacked by the defending team. The penalty for intentional grounding is usually a loss of 10 yards and causes the down to advance by one. Also if the quarterback is more than 10 yards behind the line of scrimmage the ball is just placed on the yard line where the quarterback threw the ball. Also a quarterback can avoid a penalty for intentional grounding some different ways. If there is a receiver in the area where the ball was thrown then there is no penalty for intentional grounding. The quarter is also allowed to throw the ball away, it just depends on where he is on the field.

Interception – A maneuver in which a quarterback’s pass is caught by a player on the defending team. As soon as the defending team catches the ball then that leads to an immediate change of possession. Also as soon as the possession changes then the player who caught the ball will immediately switch from the defending side to the offensive side and tries to go to their goal. Interceptions are mostly made by the secondary or the linebackers, who are usually closer to the wide receivers and the tight ends. Less frequently, the defensive lineman may get an interception if the ball is tipped, a near sack, a shovel pass, or even a screen pass. At this point when the interception is made then the other people on the defensive team immediately becomes blockers for the player who caught the ball. Also the offensive team immediately becomes the defensive team and makes an attempt to tackle the ball-carrier.

Interference – A penalty in American and Candian football in which a player interferes with a receiver's ability to make an attempt to catch a pass. Such interference could include incidents such as pushing, tripping, pulling, pulling a receiver's arms or cutting in front of him. However, it is not interference to bat away the ball so the receiver cannot catch it, not does it include catching the ball yourself so that the intended receiver does not get it. After the ball touches a defensive player or an eligible player on the offense, the interference rules do not apply and the defender may feel free to try to prevent the receiver from getting the ball; he may also tackle the receiver. In some cases, a receiver might find himself becoming a defender if a defensive player appears to have a good chance of catching a pass. In this case, the offensive player might be cited for pass interference against a defending player.

Key – In football, the word refers to a certain player, formation or anything else which indicates that the next play will be a running play. In some instances, when a team has an extremely athletic fullback kind of player, they'll put that player in motion. This means that while the QB calls out signals and before the snap, the fullback will take off running. Whenever a player is in motion, although he can run to the right or left, he cannot run across the line of scrimmage until just after the snap. When you put the fullback in motion, the defense becomes unable to tell who will guard him. At the snap, the fullback turns torward the defense and usually hits a key defender or runs to catch a fast pass.

Kick – There are four instances in a football game where kicking of the ball is required. After scoring a touchdown a team can opt to attempt an extra point by kicking the ball through the uprights. The ball is snapped to a holder (usually a back up quarterback), held in place for the kicker to attempt the point. A second instance would be when a team reaches 4th Down and instead of risking a turnover if a first down is not achieved a team can punt the ball to the opposition. A long snapper hikes the ball to the punter who dropkicks the ball to a player on the opposing team. The third instance is a kickoff. Kickoffs are done at the start of each half, after a score (touchdown, field goal), and at the start of overtime, if necessary. The ball is placed on a tee and the kicker signals when he is ready and kicks the ball in the air toward the other team. Other special teams players rush down the field to stop the opposing team from gaining yards on the kick return. During a kickoff the ball must travel at least 10 yards, such as during an onside kick or squib kick where the kicking team would try to re-claim the ball or prevent the opposing team from gaining significant yards respectively. After a safety is scored there is a free kick which is similar to a punt toward the other team.

Kicking an Opponent – a penalty that pretty much is exactly what it sounds like; results in a 15 yard penalty and possibly even ejection from the game

Kicking Game – refers to any sort of “Kick”

Kickoff – the kick that returns the ball to play at the beginning of each half and after each score

Kick Returner – A player who is on the special teams of a football team who's job is to return kicks. The player can, and most of the time does, also play on offense or defense. The kick returner sets himself up much deeper than the rest of the team so he is in position to receive the kick. When running back a kick off he usually sets himself up at around the goal line to receive the kick and follow his blockers to try and gain the most yards possible for his team so they have the shortest distance possible to score a touchdown, or field goal. When setting up for a punt return, he sets himself up about 30-40 yards behind his teammates waiting to receive the punt. If he sees that he is not going to gain any yards because the other team is close to him when the ball gets to him he can signal for a “fair catch” and he cannot be tackled and run the risk of losing possession of the football and surrendering offensive control of the ball to the other team.

Kicking an Opponent – The rules of the physical game of football do not allow players to kick each other. If such an instance were to occur the result would be a 15 yard penalty. If the penalty was committed by the defense the offense would move up 15 yards closer to the end zone. The 15 yards from the penalty would usually give the offense the yards needed for a First Down giving them a fresh set of downs to work with to try and score. If the offense commits the penalty, then they would move 15 yards further from the end zone. The 15 penalized yards on the offense would add those yards to whatever distance needed for a first down. For instance 2nd Down and 6 yards to go would become 2nd Down and 21 yards to go until the team earned a first down. If the nature of the penalty was severe enough the player could get ejected from the game as a result and could open himself up to further sanctions from the league, such as a fine and/or suspension.

Kicking Game – The kicking game of a football team is handled by the squad called the special teams. Special Teams players can also consist of players who also play on offense or defense. The special teams handles kick offs, field goals, and punts. After scoring a touchdown a team can opt to attempt an extra point by kicking the ball through the uprights. The extra point is a very short kick. The ball is snapped to a holder (usually a back up quarterback), held in place for the kicker to attempt the point. A second instance would be when a team reaches 4th Down and instead of risking a turnover if a first down is not achieved a team can punt the ball to the opposition. A long snapper, who is the Center, hikes the ball to the punter who dropkicks the ball to a player on the opposing team. Punts can be as long or short as the Punter desires and the kick does not have to stay in bounds. The other team will take possession of the ball at the spot where it goes out of bounds. The third instance is a kickoff. Kickoffs are done at the start of each half, after a score (touchdown, field goal), and at the start of overtime, if necessary. The ball is placed on a tee and the kicker signals when he is ready and kicks the ball in the air toward the other team. Other special teams players rush down the field to stop the opposing team from gaining yards on the kick return.

Kickoffs – Kickoffs are done at the start of each half, after a score (touchdown, field goal), and at the start of overtime, if necessary. The ball is placed on a tee and the kicker signals when he is ready and kicks the ball in the air toward the other team. Other special teams players rush down the field to stop the opposing team from gaining yards on the kick return. Kickoffs are usually the longest kicks of a football game. Some Kickers can kick the ball 80+ yards. If the ball is kicked into the far end zone the kick returner has the option of dropping to his knee and downing the ball. The receiving team would gain possession on their own 20 yard line. During a kickoff the ball must travel at least 10 yards, such as during an onside kick or squib kick where the kicking team tries to recover the ball or limit the yards the receiving team can get, respectively. Kickoffs must stay inbounds at all times, if the kick goes out of bounds the kicking team is penalized.