Defensive back
Defensive back (DB) is a defensive position in American and Canadian football. Defensive Backs are charged with the responsibility of preventing receivers from catching passes. However, similar to other defensive players, Defensive backs can also sack the quarterback and tackle running backs.
It should be noted that "Defensive Back" is a collective term for several other positions, which include cornerbacks, as well as Strong and Free Safeties. Alternately, this term may be referred to as the "defensive secondary".
While defensive backs must exhibit superb displays of speed and agility, they are also required to master the crucial technique of backpedaling, which enables one to follow a receiver while still focusing on the football. Furthermore, Defensive backs must be able to analyze an offensive formation before the play can begin, allowing one to predict intentions of an offense. A defensive back must also possess the ability to change one's path while running at whim, enabling a superior "man-to-man" coverage. Lastly, a defensive back must be capable of voraciously and accurately tackling offensive units. While these tackles may not often make the highlight reel after the game, they prevent the offensive units from breaking away and making big plays.
Safeties
The safety is positioned 10 to 15 yards behind the line of scrimmage, depending on the safety's speed. There are usually two safeties per play, which are placed on opposite ends of a formation. However, if a defensive play may only require one safety, the player is usually positioned in the center of the formation. The safety provides the final line of defense against running backs and receivers who elude the linebackers and cornerbacks. Usually, a safety is agile, dexterous, vigilant, and capable of predicting the offense's next play just by looking at their formation.
The free safety (FS) is responsible for reading the offensive plays and covering deep passes. Depending on the defensive call, the safety may also provide run support.
The strong safety (SS) is usually larger than the free safety, and is positioned relatively closer to the line of scrimmage. While strong safeties play a pivotal role in halting the offense's running game, they are also responsible for keeping various receivers, especially tight ends, in check.
Cornerbacks
Cornerbacks (CB) position themselves at the line of scrimmage, directly opposite to the wide receivers. Cornerbacks attempt to disrupt the receivers' routes. They are often the fastest and most acrobatic players on the defense. Occasionally, one of the cornerbacks may be required to abandon their coverage of a receiver, and instead surprise the offense by rushing the quarterback.
If the defense expects a pass, they may replace one or two of the linebackers with additional defensive backs. The fifth defensive back is called the nickel back, and the sixth is called the dimeback.
Statistics for defensive backs include interceptions, tackles, and passes deflected.