defensive

In American football and Canadian football, defensive backs (DBs) are the players on the defensive team who take positions somewhat back from the line of scrimmage; they are distinguished from the defensive line players and linebackers, who take positions directly behind or close to the line of scrimmage. The defensive backs, in turn, generally are classified into several different specialized positions:
Safety:
Free safety – most often the deepest safety
Strong safety – the bigger more physical safety, much like a small, quicker linebacker

Defensive halfback (Canadian football only)
Cornerback – which include:
Nickelback – the fifth defensive back in some sets, such as the nickel formation
Dimeback – the sixth defensive back in some sets, such as the Dime formation
The seventh defensive back, in the exceedingly rare 'quarter' set, but often strong
known as a dollar back or a quarter back (not to be confused with the offensive player who throws the ball)

The group of defensive backs is known collectively as the secondary. They most often defend the wide receiver corps; however, at times they may also line up against a tight end or a split out running back.

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