Intentional grounding is a penalty in football that is called on the offensive team when the passer intentionally throws the ball incomplete while under pressure from the defense in order to avoid a sack. An intentional grounding penalty is called when the ball does not pass the line of scrimmage and goes out of bounds, or hits the ground before reaching the line of scrimmage without an eligible receiver nearby. This results in a 10-yard penalty and a loss of down for the offense.
A spike is not considered an intentional grounding penalty unless the quarterback is under pressure from the defense. Because during a spike the defense usually never has enough time to cross the line of scrimmage, it is a legal play. However, if the quarterback waits on the defense to get closer before performing the spike, an intentional grounding penalty may be called.