Gaps in football are the spaces between the offensive line players. Gaps are really important in football games, and for coaching purposes, each gap has a name which is based on the players around the gap. The space between the center and the guards is called A-gap, and the one between the guards and the tackles is the B-gap. Further up on the line of scrimmage there is the C-gap, which is the space between the tackles and tight ends, and the D-gap, the last space between the tight end and the sidelines.
Discipline is crucial for a team to be successful when attacking and defending the gaps. The gaps are the spaces where the offense will go through to run with the ball, and where the defense will try to get through and get to the quarterback. That way is the defensive does not have control over the gaps, the opposing offense will be able to easily run with the ball, and the quarterback will hardly ever feel pressured; and if the offensive line does not have control over them, the quarterback will be easily sacked and pressured; and the team's offense will not be able to run well and rely heavily on passing.