The defensive team or defense in American football or Canadian football, is the team that begins a play from scrimmage not in possession of the ball.

Unlike the offensive team, there are no formally defined defensive positions. A defensive player may line up anywhere on his side of the line of scrimmage and perform any legal action. However, most sets used in American football include a line composed of defensive ends and defensive tackles and, behind the line, linebackers, cornerbacks, a strong safety and a free safety.

• defensive end - the two defensive ends play on the outside of the defensive line. Their function is to rush the passer or stop runs. The faster of the two is usually placed on the right because this is a right-handed quarterback's blind side.
• defensive tackle - (sometimes called a defensive guard), defensive tackles are linemen who line up inside the defensive ends. Their function is to rush the passer and defend against running plays. A defensive tackle that lines up directly across from the ball (on the nose of the center) is often called a nose tackle. Common defensive sets have from one to three defensive tackles.
• linebacker - linebackers play behind the defensive line and perform various duties depending on the situation, including rushing the passer, covering receivers, and defending against the run. Most defensive sets have between three and five linebackers. Linebackers are usually divided into three types, strongside, middle, and weakside. The strongside linebacker, (nicknamed "Sam"), usually lines up across from the tight end and is usually the strongest because he must be able to shed lead blockers to tackle the running back. The middle linebacker ("Mike" or "Mack"), is the quarterback of the defense, he must call out offensive formations and what adjustments the defense must make. The weakside linebacker ("Will"), is usually the most athletic linebacker because he usually must play an open field.
• cornerback - the cornerbacks primarily cover the wide receivers.
• safety - the safeties are the last line of defense (farthest from the line of scrimmage), and provide help on deep pass coverage. There are generally two types of safeties, strong and free. The strong safety is usually the larger and stronger of the two and provides extra run support. The free safety is usually the smaller and faster of the two and provides extra pass support. However more recently teams are looking for more hybrid safeties who can provide both run and pass support.
• nickel and dime backs - in certain formations an extra fifth defensive back (called 'nickel' since a nickel coin has the value of five cents) or even a sixth (called 'dime' since a dime is equal to two nickels) may be used to augment the backfield in situations where a long pass is expected.

See also

• American football defensive schemes
• Lineman (football)
• Defensive back
• Offensive team
• Special teams
• Glossary of American football