A position on defense that lines up behind the defensive line. The linebackers need to be versatile as they can be responsible for all facets of the defense, including run support, pass rush and pass coverage. Linebackers tend to make the most tackles on the defense, since they are the least likely to be blocked by the offensive line at the beginning of a play. Teams can have anywhere between one to four linebackers on the field at a time depending on the alignment of the defense on a particular play.
The linebacker is the middle level of the defense. Linebackers often need to have a blend of size and strength due to the nature of the position. On any given play, a linebacker can find himself tackling a running back, guarding a pass receiver or blitzing the quarterback.
The linebackers tend to be considered the leaders of the defense and are often responsible for making reads and adjusting the defense in response to a particular offensive alignment. The number of linebackers on any given play can change depending on the number of wide receivers the offense chooses to play, since linebackers tend to be mismatched when guarding them. The linebackers are also the primary individuals responsible for blitzing the quarterback, since they can come from behind the defensive line and find a hole through the pass protection to get to the quarterback.