Offensive Line

In gridiron football, a lineman is a player who specializes in play at the line of scrimmage. The linemen of the team currently in possession of the ball are the offensive line, while linemen on the opposing team are the defensive line. A number of NFL rules specifically address restrictions and requirements for the offensive line. The defensive line is covered by the same rules that apply to all defensive players and the offensive lineman are supposed to help block the quarterback from getting sacks for a loss or even worse a fumble. Linemen are usually the largest players on the field in both height and weight, since their positions usually require less running and more strength than skill positions.

An offensive lineman's motion during a play is often limited to just a few quick steps to establish position, followed by a wrestling match similar to sumo. Offensive linemen thus tend to be the largest players on the field, with excellent agility and balance but limited straight-line running speed. Most pro and college football offensive lineman tend to weigh over 300 pounds.

On running plays, the primary job of the offensive line is to create space for the ball carrier to run, either by pushing all defensive players backwards past the line of scrimmage, or by pushing defensive players to the side to allow the ball carrier to run past them.

On passing plays, the offensive line is responsible for stopping defensive players from tackling the quarterback before he has thrown the ball. Stopping these players indefinitely is usually not possible, so the main objective of the offensive line is to slow them down, providing the quarterback with several seconds to identify an open receiver and throw the ball.

The interior offensive line consists of the center, who is responsible for snapping the ball into play, two guards who flank the center, and two offensive tackles who flank the guards. In addition to the interior line, a full offensive line may also include a Tight End outside one or both of the tackles.

Interior offensive linemen are not eligible to catch forward passes, and are not allowed to advance more than 2 yards past the line of scrimmage at the time a pass is thrown, whether they are engaged with a defensive player or not. However, ends (whether tight ends or wide receivers) are eligible to catch passes.

...
Wikipedia