In football, a dime defense refers to a defensive play that uses six defensive backs. Dime defense is also commonly referred to as a dime set, dime coverage, or dime package. A typical set of defensive personnel includes only four defensive backs (two safeties and two cornerbacks), so a dime set replaces two linemen or linebackers with cornerbacks or safeties.
The term "dime" is derived from a different defensive set called the "nickel" (because it includes five defensive backs and a nickel is worth five cents). A dime is one step up from a nickel in currency, so the name for a defense that adds another DB to a nickel is the "dime." Just as the fifth defensive back in a nickel is called a nickelback, the sixth DB in a dime set is a dimeback.
The dime defense is used to defend obvious passing situations or spread offense formations. This is because more defensive backs are needed to cover extra wide receivers. Although it is used less often than a nickel defense, the dime is still a common knowledge and terminology among coaches, players, and analysts.
Technically, any defensive formation that includes six defensive backs can be referred to as a dime package. However, there are some common formations that the dime is used in. One of these is the 4-1-6, which leaves only one linebacker to cover a running back or keep an eye on the quarterback while maintaining four linemen to apply pressure on the QB. The other main dime formation, the 3-2-6, is less concerned with rushing the pocket and more with keeping tighter coverage in the secondary.
When a defense knows an offense needs to throw the ball, the dime defense allows more coverage of receivers, making it much harder for the quarterback to complete a pass. The extra defensive backs also prevent big plays because they are often farther off the line of scrimmage.
While the dime is great for defending obvious pass plays, it can leave a defense extremely vulnerable to runs. Replacing bigger, stronger linemen and linebackers with smaller, quicker DBs makes tackling and getting through blocks much more difficult for a defense. Lining up in a dime package also spaces the defense out more, rather than keeping more players up toward the line of scrimmage and tackle box.