Quarterbacks

A good quarterback and a great quarterback can be separated most easily through a few categories: interceptions, touchdowns and completion percentage. As of January 2010, Matt Hasselbeck has thrown 164 touchdowns and 111 interceptions in his career and has a 60% completion rate. Joe Montana threw 273 touchdowns and 139 interceptions and had a 63% rate.

Running Backs

Speed and strength, which make the difference between a good running back and a great running back, are measured most easily in yardage gained in a season and over a career. A good running back such as Shaun Alexander can win an MVP award for a single year, but his 9,453 career yards can't touch Barry Sanders' 15,269.

The Offensive Line

Observers judge an offensive lineman by his sturdiness at the line. His strength and footwork are the key components to his success. A good lineman simply stops a defender, but a great lineman blocks through a defender, knocking him on the ground. A great lineman also can deliver the lead block on running plays.

The Defensive Line and Linebackers

On the defensive side, speed, strength, and instincts make the difference. Good players get a few sacks and often lead their team in tackles for a season, but great players lead in the National Football League in tackles each season, because they instinctively find the ball carrier.

The Defensive Backfield

Interceptions and passes defended offer the easiest way to measure greatness in cornerbacks. Deion Sanders blanketed receivers while catching 93 interceptions in his career, while Sam Madison caught only 39.

Source:

Pro Football Reference