The four across defense, also known as a 4-4 defensive formation, is a type of defensive lineup that includes four defensive linemen and four linebackers. This is an introductory level formation and is commonly used among younger age and league levels.
The Four Across Defense consists of defensive linemen and linebackers, both with different roles. The defensive linemen play opposite of the team at the line of scrimmage. They typically pick one man to defend after the ball is snapped. They stop the offensive team from breaking through the defense, finding an open lane and getting open for a scoring opportunity.
Defensive linemen need to be strong and large in size, as their main role is to stop the other team from gaining any advantages on the field.
The linebackers are positioned behind the defensive linemen. They act as "backup" defenders. If any offensive member breaks through the linemen, the linebackers are there to stop them. Although they serve as backup defenders, their roles are vital to any team, especially the defense. Linebackers are considered the most important defensive player as they are very versatile. Some plays they serve as blockers, others they serve as extra pass protectors. Because of this, linebackers should be strong but also quick. Their size shouldn't inhibit their ability to have quick feet on the field.
The 4-4 is often deemed as a weak formation, only because it is simple in structure and easy for opponents to quickly adapt to. It doesn't give much defensive variety on the field. This is why many coaches choose to train younger players in the four across defense. It is easy to learn and very valuable once a player learns deviations of this formation.