stopping the run, while others are fast and agile, and are much better at rushing the quarterback than stopping the run. Linebackers Linebackers stand behind the defensive linemen or set themselves up on the line of scrimmage. Depending on the type of defensive strategy being used, a linebacker's responsibilities can include helping to stop the run, rushing the quarterback, or dropping back in pass protection. Outside linebackers: The outside linebackers ("OLB") set up on the outside portion of the line of scrimmage. They are often used to rush the quarterback. OLBs tend to be the fastest and most agile linebackers on the defense. Inside linebackers: Inside linebackers ("ILB"), sometimes also referred to as middle linebackers ("MLB") set up on the inside portion of the line of scrimmage. ILBs tend to be the biggest and strongest linebackers on the defense. Defensive backs Defensive backs stand behind the linebackers. Their primary responsibility is pass coverage, although they can also be involved in stopping the run or rushing the quarterback. Cornerback: The cornerback ("CB") lines up opposite the opposing offense's wide receiver(s). Their main job is to cover wide receivers and prevent them from catching passes, or tackle them if they do. Safety: A defense's safeties ("S") are usually the farthest away from the line of scrimmage when the play starts. Their job is to help the cornerbacks cover receivers and, if necessary, help the defensive line and linebackers protect against the run. Because of this "do everything" role, most safeties are the best all-around athletes on the defense. Safeties are designated as strong safeties ("SS") or free safeties ("FS"). The strong safety typically plays closer to the line, matches up against tight ends, and is more involved in the run, while the free safety typically is farther from the line and plays more of a "last line of defense" role in both the pass and run game. Defensive formations The most common way to describe a basic defensive formation is by stating the number of linemen involved followed by the number of linebackers. The number of defensive backs is usually not mentioned, though if it is, (such as in the "3–3–5"), the number typically appears after the number of linebackers, thus the formula would go (# of linemen)–(# of linebackers)–(# of defensive backs [if stated]) in these situations. This naming rule does not always apply when the personnel for a certain formation