Things began to change in the mid-1950s when Tom Landry became defensive coordinator of the New York Giants and introduced the word "key" to the football vernacular.

"When I am analyzing a particular offense, I try to determine what the offensive coach has in his mind, what he is trying to accomplish," Landry once said. "Then I can develop defensive techniques that will neutralize his strength."

Tom Landry's climb to the Hall of Fame began as the mastermind of the Giants defenses of the 1950s.(AP)

It was a highly technical approach, and it worked wonders. The Giants won one NFL championship (1956) and played in two other titles games (1958, '59) in a four-year stretch before Landry left to become the first head coach of the Dallas Cowboys in 1960. And even after Landry's departure, his sound principles remained the cornerstone of the Giants defense, and New York qualified for the NFL championship game three years in a row (1961-63).

Landry had been a good defensive back for the Giants from 1950-55, but when Jim Lee Howell took over as head coach in 1954, he recognized Landry's greatest attribute was the way he prepared and studied. Thus, he made Landry a player/coach in 1954, and Landry turned to coaching full-time in 1956.

Landry spent hours and hours breaking down opponents' tendencies, and it got to the point where he could predict every play just by knowing the percentages of what teams did in certain situations. Thus, when preparing the Giants for a game, he assigned specific tasks for each player against every play he expected the opposition to run.

He took the guesswork out of defense. In his system, rather than react to what was happening, Landry's defenders usually knew ahead of time - based on formations and tendencies - what was going to happen. Using particular keys, each player carried out his assignment, turning the defensive team into a complex and coordinated unit.

"Tom Landry was the only coach I knew who knew what he was doing all the time," said defensive end Andy Robustelli, who came to New York in a trade from Los Angeles in 1956 and helped the Giants win the championship that year. "We had the ability to adjust. That's what made Tom as a coach and us as a team."

In 1956, Robustelli led an influx of new, talented players who joined the Giants. Like Robustelli, defensive tackle Dick Modzelewski and cornerback Ed Hughes were acquired in trades; linebacker Sam Huff and end Jim Katkavage were drafted; and tackle Rosey Grier and safety Jimmy Patton were already in place. All of these men played vital roles in the implementation of Landry's inside 4-3 defense that turned the Giants' fortunes around.

Huff, the tough-guy middle linebacker who would ultimately join Robustelli in the Pro Football Hall of Fame, was the hub of the unit.

"Huff was a fantastic middle linebacker when we were playing the 4-3 inside defense," Robustelli said. "He was taking keys. The halfback goes that way, he fills the 5-hole, he goes the other way, he fills the 4-hole. We were filling holes so good that the offense had to do something to stop us from our inside defense."

Early in his career, Huff and Landry lived during the season at the Concourse Plaza Hotel in the Bronx a couple blocks from Yankee Stadium, and Huff often spent his evenings sitting at Landry's kitchen table drawing up alignments and going over strategy for upcoming opponents.

"Every night he'd call me down," Huff said. "He was putting together the 4-3 defense that made him so famous. He built it around me. I'd tell him what I thought I could do and what I couldn't do. He wanted to know, and he wanted me to be totally honest with him. And he never did anything that I couldn't do.

"It was designed for me to make the tackles. It was probably the first coordinated defense in football. You'd read your keys depending on what the offense was showing you and react to what you saw. All 11 guys had to play that defense. There was no freelancing, and if one guy broke down, the whole thing broke down. But it didn't happen very often. He explained everything, he drilled it into us, and we made it work to our advantage."

In that first year of the 4-3, the Giants put together a five-game midseason winning streak that was enough to win the Eastern Division, and they proceeded to rout the mighty Bears 47-7 for their first NFL championship since 1938. The Giants stifled Chicago's potent running game, limiting it to 67 yards as Huff battered running back Rick Casares all day.

After a 7-5 letdown in 1957, the Giants won the East in '58 and '59, but both years lost to the Baltimore Colts in the NFL title game. Had they won either or both, their defense would have been considered one of the greatest of all-time. Instead, it must settle for being recognized as one of the most revolutionary in the history of the game.

"More than any defense I ever played against, New York played team defense," Cleveland Hall of Fame running back Jim Brown said. "They were football's version of the Boston Celtics. Each guy's responsibility was related to the next guy's. The Giants had one of the stingiest defenses in football."