I Formation – an offensive formation where both of the “Backs” lineup directly behind the “Quarterback” in an alignment that resembles an “I”

Illegal Formation – in the NFL, this is an offensive formation in which less than seven players are lined up on the “Line of Scrimmage”

Illegal Motion – a five yard penalty resulting from two offensive players being in motion at the same time at the “Snap” of the ball

Illegal Procedure – See “False Start”

Illegal Shift – a five yard penalty 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

In Bounds – the area of the field between the “Sidelines” and “Endlines”

Incomplete Pass – a “Pass” attempt that doesn’t reach the “Receiver” before it hits the ground, or one that gets to the receiver “Out of Bounds”

Incompletion – See “Incomplete Pass”

Intentional Grounding – a 10 yard penalty resulting when the “Quarterback” – while still inside the “Pocket” -- intentionally throws the ball into the ground or out of bounds away from any eligible receivers, usually to avoid a “Sack”

Interception – a pass caught by a defender, which results in a change in possession

Interference – an illegal maneuver that unfairly hampers a “Receiver” from catching a “Pass”

Key – a formation, a certain player, or something else that indicates the play is going to be a running play 

Kick – an attempt at punting, kicking a “Field Goal” or a “Kickoff”

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 on the “Special Teams” squad who runs back “Kickoffs” or “Punts”