Casual football fans may be familiar with the terms "lineman" and "linebacker" in reference to positions, but not know exactly which players line up where and what their responsibilities are. The exact formation and duties of lineman and linebackers vary depending on the scheme and formation the team is running.
Who Plays Where
The two most common defensive schemes in professional football are the 3-4 and 4-3, which designates how many linemen and linebackers, respectively, are on the field at one time. The 3-4 scheme entails three linemen and four linebackers behind them, while the 4-3 scheme plays with three linebackers and four linemen. Both schemes have four defensive backs to round out the 11 players on the defensive side of the ball. There are also five linemen on the offensive side of the ball, who protect the quarterback and try to make holes for the running backs to run through.
What Linemen Do
Linemen are typically very large players, often upward of 300 pounds. Defensive linemen are typically broken up into two groups, tackles and ends. Tackles play in the middle of the defensive line, charged with clogging up the middle of the field to prevent running backs from gaining yards going straight forward, as well as trying to push the offensive linemen backward and to collapse the pocket on passing plays. Defensive ends typically have the role of containing the run toward the outside and pressuring the quarterback in an attempt to record a sack.
The Role of Linebackers
Linebackers are classified as Mike, Will or Sam linebackers, which is a shorthand way of saying middle, weak side and strong side linebackers. Both 3-4 and 4-3 schemes have weak side and strong side linebackers, with the strong side being the side of the field that corresponds with the quarterback's dominant hand. There is only one middle linebacker when there are three linebackers on the field, and two middles in a 3-4 scheme. The linebackers are charged with filling gaps that happen in the line and preventing receivers from running freely across the middle of the field.
Check the Numbers
The numbering system adopted by the NFL can help you differentiate between linemen and linebackers as well. Guards and tackles on the offensive line wear numbers 60 through 79, and centers are allowed to wear 50 to 59 as well. Defensive linemen are required to wear between 60 and 79 or between 90 and 99, whereas linebackers have to wear numbers between 50 and 59 or 90 to 99. The system is not foolproof in differentiating a lineman from a linebacker as there is some overlap, but it can help you tell who is who on the defensive side of the ball.