1869:
Rutgers and Princeton played a college soccer football game, the first ever, November 6. The game used modified London Football Association rules. During the next seven years, rugby gained favor with the major eastern schools over soccer, and modern football began to develop from rugby.

1876:
At the Massasoit convention, the first rules for American football were written. Walter Camp, who would become known as the father of American football, first became involved with the game.

1898:
A touchdown was changed from four points to five.

1904:
A field goal was changed from five points to four.

1906:
The forward pass was legalized. The first authenticated pass completion in a pro game came on October 27, when George (Peggy) Parratt of Massillon threw a completion to Dan (Bullet) Riley in a victory over a combined Benwood -Moundsville team.

1909:
A field goal dropped from four points to three.

1912:
A touchdown was increased from five points to six.

1933:
The NFL, which long had followed the rules of college football, made a number of significant changes from the college game for the first time and began to develop rules serving its needs and the style of play it preferred. The innovations from the 1932 championship game-inbounds line or hashmarks and goal posts on the goal lines-were adopted.

 The forward pass was legalized from anywhere behind the line of scrimmage.

1941:
The league by-laws were revised to provide for playoffs in case there were ties in division races, and sudden-death overtimes in case a playoff game was tied after four quarters. An official NFL Record Manual was published for the first time.

1945:
The inbounds lines or hashmarks were moved from 15 yards away from the sidelines to nearer the center of the field-20 yards from the sidelines.

1946:
Free substitution was withdrawn and substitutions were limited to no more than three men at a time.

 Forward passes were made automatically incomplete upon striking the goal posts.

1948:
Plastic helmets were prohibited.

 A flexible artificial tee was permitted at the kickoff.

1949:
Free substitution was adopted for one year.

1950:
Unlimited free substitution was restored, opening the way for the era of two platoons and specialization in pro football.

1951:
The Pro Bowl game, dormant since 1942, was revived under a new format matching the all-stars of each conference at the Los Angeles Memorial Coliseum. The American Conference defeated the National Conference 28-27, January 14. A rule was passed that no tackle, guard, or center would be eligible to catch a forward pass.

1955:
The sudden-death overtime rule was used for the first time in a pre-season game between the Rams and Giants at Portland , Oregon , August 28. The Rams won 23-17 three minutes into overtime.

 A rule change declared the ball dead immediately if the ball carrier touched the ground with any part of his body except his hands or feet while in the grasp of an opponent.

1956:
Grabbing an opponent's facemask (other than the ball carrier) was made illegal.

Using radio receivers to communicate with players on the field was prohibited.

A natural leather ball with white end stripes replaced the white ball with black stripes for night games.

1960:
The AFL adopted the two-point option on points after touchdown.

1962:
Both leagues [NFL & AFL] prohibited grabbing any player's facemask.

The AFL voted to make the scoreboard clock the official timer of the game.

1966:
Goal posts offset from the goal line, painted bright yellow, and with uprights 20 feet above the cross-bar were made standard in the NFL.

1967:
The "sling-shot" goal post and a six-foot-wide border around the field were made standard in the NFL.

1969:
The AFL established a playoff format for the 1969 season, with the winner in one division playing the runner-up in the other.

1970:
The merged 26-team league [NFL] adopted rules changes putting names on the backs of players' jerseys, making a point after touchdown worth only one point, and making the scoreboard clock the official timing device of the game.

1972:
The inbounds lines or hashmarks were moved nearer the center of the field, 23 yards, 1 foot, 9 inches from the sidelines.

The method of determining won-lost percentage in standings changed. Tie games, previously not counted in the standings, were made equal to a half-game won and a half-game lost.

1973:
A jersey numbering system was adopted, April 5: 1-19 for quarterbacks and specialists, 20-49 for running backs and defensive backs, 50-59 for centers and linebackers, 60-79 for defensive linemen and interior offensive linemen other than centers, and 80-89 for wide receivers and tight ends. Players who had been in the NFL in 1972 could continue to use old numbers.

1974:
Sweeping rules changes were adopted to add action and tempo to games: one sudden-death overtime period was added for pre-season and regular-season games.

The goal posts were moved from the goal line to the end lines.

Kickoffs were moved from the 40- to the 35-yard line.

After missed field goals from beyond the 20, the ball was to be returned to the line of scrimmage.

Restrictions were placed on members of the punting team to open up return possibilities.

Roll-blocking and cutting of wide receivers was eliminated; the extent of downfield contact a defender could have with an eligible receiver was restricted.

The penalties for offensive holding, illegal use of the hands, and tripping were reduced from 15 to 10 yards; wide receivers blocking back toward the ball within three yards of the line of scrimmage were prevented from blocking below the waist.

1976:
Owners adopted the use of two 30-second clocks for all games, visible to both players and fans to note the official time between the ready-for-play signal and snap of the ball.

1977:
A 16-game regular season, 4-game preseason was adopted to begin in 1978.

A second wild-card team was adopted for the playoffs beginning in 1978, with the wild-card teams to play each other and the winners advancing to a round of eight postseason series.

Rule changes were adopted to open up the passing game and to cut down on injuries.

Defenders were permitted to make contact with eligible receivers only once; the head slap was outlawed; offensive linemen were prohibited from thrusting their hands to an opponent's neck, face, or head; and wide receivers were prohibited from clipping, even in the legal clipping zone.

1978:
The NFL continued a trend toward opening up the game. Rules changes permitted a defender to maintain contact with a receiver within five yards of the line of scrimmage, but restricted contact beyond that point. The pass-blocking rule was interpreted to permit the extending of arms and open hands.

1979:
NFL rules changes emphasized additional player safety. The changes prohibited players on the receiving team from blocking below the waist during kickoffs, punts, and field-goal attempts; prohibited the wearing of torn or altered equipment and exposed pads that could be hazardous; extended the zone in which there could be no crackback blocks; and instructed officials to quickly whistle a play dead when a quarterback was clearly in the grasp of a tackler.

1980:
Rules changes placed greater restrictions on contact in the area of the head, neck, and face.

Under the heading of "personal foul," players were prohibited from directly striking, swinging, or clubbing on the head, neck, or face. Starting in 1980, a penalty could be called for such contact whether or not the initial contact was made below the neck area.

1988:
At the NFL annual meeting in Phoenix , Arizona , a 45-second clock was also approved to replace the 30-second clock. For a normal sequence of plays, the interval between plays was changed to 45 seconds from the time the ball is signaled dead until it is snapped on the succeeding play.

1990:
The NFL revised its playoff format to include two additional wild-card teams (one per conference).

1994:
There is now a 2 point conversion following touchdowns (teams now have the option of passing or running for two points or kicking for one after a TD).

The starting point of all kickoffs will be the kicking teams 30 yard line (moved back 5 yards).

Kickoff tees used can be no more than one inch in height (previously 3 inches).

A neutral zone infraction has been clarified (officials are to immediately blow their whistles whenever a defender enters the neutral zone causing the offensive player(s) directly opposite to move, this is considered a penalty on the defense. If there is no immediate reactional movement by the offensive player(s), there is no foul. (The neutral zone is defined as the space the length of the ball between the offense and defense line of scrimmage).

All field goals attempted and missed when the spot of the kick is beyond the 20 yard line, the defensive team taking possession will get the ball at the spot of the kick.

On any field goal attempted and missed with the spot of the kick is on or inside the 20, the ball will go to the defensive team taking possession at the 20.

The 11 players on the receiving team are prohibited from blocking below the waiste during a play in which there is a kickoff, safety kick, punt, field goal attempt or extra point kick with one exception, immediately at the snap on these plays those defenders on the line of scrimmage lined up on or inside the normal tight end position can block low.

1995:
The emergency (third) quarterback may now enter the game in just the fourth quarter, regardless if the other two quarterbacks are able to play. This means that if the third string quarterback enters the game, the first and/or second quarterback may re-enter, unlike the past two seasons where the emergency quarterback would only play off the first two were unable to resume play.

 Quarterbacks may now receive communication from the bench via a small radio transmitter in their helmets. This proposal was originally run on a test basis last year during the pre-season, but was scrapped.

1996:
The five-yard contact rule will be enforced more stringently.

Hits with the helmet or to the head by the defender will be flagged as personal fouls and subject to fines. This is being done to protect the offense, particularly the quarterback.

1997:
When a team fakes a punt and throws the ball downfield, pass interference calls on the two outside defenders who are actually trying to block a coverage man from getting downfield and might not even know the ball has been thrown have been eliminated.

No player may remove his helmet while on the playing field. Doing so will result in a 15-yard unsportsmanlike conduct penalty. Exceptions are during timeouts and between quarters. (The NFL has done this in an effort to "reduce taunting and overexuberant celebrations" and also "in the name of safety.")

1998:
The coin toss will be called before the coin itself is tossed (this is a mid-season change).

Tinted visors are banned from players' facemasks except for medical need.

A team will be penalized immediately for having twelve players in a huddle even if the 12th player goes straight to the sideline as the huddle breaks.

A defensive player can no longer flinch before the snap to draw movement from an offensive linemen.

 nstant Replay was turned down again.

1999:
Instant replay returns with a challange system.

Clipping is now illegal around the line of scrimmage just as it is on the rest of the field.

2000:
Instant replay renewed with the same rules.

Celebrations limited to one player. Fines will be assessed for celebrations by two or more players.

Off-Field supervisory titles elminated , preventing coaches from changing teams without becoming head coach, or "in cases where it's written into individual contracts."

Off-Field consolidation of the sport's internet presence into NFL.com. Teams would evenly split the proceeds.

Anyone wearing an eligible number (1-49 and 80-89) can play at quarterback without having to check in with the referee.

2001:
Instant replay renewed for three years with the same rules.

Fumble recoveries will be awarded at the spot of the recovery, not where the player's momentum carries him.

Protecting the passer will be emphasized even more.

Taunting rules will be tightened, with 15-yard unsportsmanlike-conduct penalties flagged.

Bandannas and stocking caps are out, but skullcaps with the team colors and logos are OK.

2002:
A player who touches a pylon remains in-bounds until any part of his body touches the ground out-of-bounds.

Continuing-action fouls now become dead-ball fouls and will result in the loss of down and distance.

Any dead-ball penalties by the offense after they have made the line to gain will result in a loss of 15 yards and a new first-and-10 series.

The act of batting and stripping the ball from player possession is legalized.

The chop-block technique is illegal on kicking plays.

It is illegal to hit a quarterback helmet-to-helmet anytime after a change of possession.

After a kickoff, the game clock will start when the ball is touched legally in the field of play; the two-minute exception is eliminated.

Inside of two minutes, the game clock will not stop when the player who originally takes the snap is tackled behind the line of scrimmage.

2003:
Officials will be kept together as a single crew during the playoffs. This is a change from past seasons when "all-star" officiating crews worked the post season.

2004:
Instant replay was extended for five years and adjusted to give teams an extra challaenge if both previous challanges were successful.

"Flamboyant" celebrations will be penalized automatically for 15 yards.

Wide receivers allowed to wear numbers 11-19 for the increased amount of retired numbers, as well as more players at wide receiver and tight end (who also wear numbers in the 80s) coming into the league.

2005:
The "horse-collar tackle", in which a defender grabs inside the back or side of an opponent's shoulder pads and pulls that player down, is prohibited. Named the "Roy Williams Rule" after the Dallas Cowboys defensive back whose horse-collar tackle during the last season caused a serious and nearly season-ending injury to Philadelphia Eagles wide receiver Terrell Owens.

Peel-back blocks (where an offensive player blocks a defender who is moving back toward the direction of his own end zone) below the waist and from the back are now illegal.

Unnecessary roughness would be called for blocks away from the play on punters or kickers, similar to the same protection quarterbacks have after interceptions.

When time is stopped by officials prior to the snap for any reason while time is in, the play clock resumes with the same amount of time that remained on it - with a minimum of 10 seconds. Previously, the play-clock would be reset to 25 seconds.

During field goal and extra point attempts, the defensive team will be penalized for unsportsmanlike conduct if it calls consecutive timeouts in an attempt to "ice" the kicker. Previously, the second timeout request was only denied by officials, and thus could be used to distract the kickers.

Players cannot run, dive into, cut, or throw their bodies against or on an opponent who is out of the play or should not have reasonably anticipated such contact.

If the defensive team commits a dead ball foul following the end of the half, the offensive team may choose to extend the period for one more play. Previously, the half automatically ended without the defensive team being penalized.

During a punt, if the kicking team illegally touches the ball inside the 5-yard line, the receiving team has the option of either treating the result as a touchback or replaying the down with a 5-yard penalty against the kicking team. Previously, the receiving team's only options were either the latter or taking over possession at the spot of the foul. This change prevents an ineligible player from keeping a kick from entering the end zone and becoming a touchback.

If the kicking team commits a penalty, the receiving team can have the option of adding five yards to the return or taking a penalty and forcing the kicking team to rekick the ball. Previously they could take the latter or decline the penalty.

If a team calls for an instant replay challenge after it has used all its challenges or is out of timeouts, it will be assessed an unsportsmanlike conduct penalty. The penalty will also be assessed if a team calls for a challenge inside of two minutes of either half or overtime, when only the replay assistant can initiate reviews. Previously, the request was only denied by the Referee. This change was made to prevent head coaches from constantly stopping the game for any reason, including to just argue with the Referee.

Teams are only able to request an instant replay challenge by tossing their red flag to get the attention of officials. The league decided to do away with the electronic pager/vibrating alert system used by head coaches because practically all of them always used their red flags instead of their pagers anyway. (However, the replay assistant will still use the pagers to notify the officials of a replay request).

2006:
End zone celebrations are more restricted. Players cannot celebrate by using any type of prop, or do any act in which they are on the ground. Players may still spike, spin the ball, or dunk it over the goal posts. Dancing in the end zone is also permitted as long as it is not a prolonged or group celebration.

Defenders are prohibited from hitting a passer in the knee or below unless they are blocked into him. This rule was enacted in response to the previous season's injuries to Cincinnati Bengals quarterback Carson Palmer, Pittsburgh Steelers' Ben Roethlisberger , and Tampa Bay Buccaneers' Brian Griese .

Down-by-contact calls can now be reviewed by instant replay to determine if a player fumbled the ball before he was down, and who recovered it. Previously, these plays could not be reversed once officials blew the whistle.

The "horse-collar tackle" rule enacted during the previous 2005 season is expanded. Players are now prohibited from tackling a ball carrier from the rear by tugging inside his jersey. Previously, it was only illegal if the tackler's hand got inside the player's shoulder pads.

To reduce injuries, defensive players cannot line up directly over the long snapper during field goal and extra point attempts.

2007:
INSTANT REPLAY: Made a permanent rule.

INSTANT REPLAY: Also made permanent in the replay system were “down-by-contact” as a reviewable play and each review being limited to a maximum of 60 seconds.

SPIKING OF BALL: It will now be a five-yard penalty for a player to spike or throw the ball after a down has ended, except for after a touchdown.

PLAYER SAFETY: It will now be a 15-yard penalty (rather than five yards) for a player to make a block below the waist against an eligible receiver while the quarterback is in the pocket. Also, when a player who receives the snap fumbles or muffs the ball, the restrictions on the defensive team relative to illegal contact and an illegal cut- block will end.

TWO-MINUTE WARNING/10-SECOND RUNOFF: The requirement that the offense has to be behind in the score or the score has to be tied for a 10-second clock runoff to be exercised against the offense for an excess timeout with two minutes to go in the first half or in the game has been eliminated. Now a 10-second runoff will take place no matter what the game situation. Any possible advantage for the offense (e.g., the old rule would not require a 10-second runoff if it were ahead) has been eliminated. The defense has the option to decline a 10-second runoff (which will give it more time should it get the ball back).

CLOCK STOPPAGE: Two exceptions were added to the rule that dictates that the play clock be restarted at the time at which it was stopped prior to the snap. Now an instant replay review prior to the two-minute warning will reset the clock at 25 seconds (as has been the case with other stoppages such as a penalty), as will an instant replay review after the two-minute warning that results in a reversal. These changes will make the administration of the rule more consistent.

PACE OF GAME: The foul for unintentional touching of a forward pass by an interior lineman has been eliminated. It was felt that no advantage was gained by the offense on such a play, and elimination of the rule would speed up the game.

CROWD NOISE: The five-yard penalty against the defense for excessive crowd noise has been eliminated. The penalty had not been called in many years.

ASSISTANCT COACH INTERVIEWS: Assistant coaches on Super Bowl teams may now interview for a second time with a club for its head-coaching position during the off-week after the championship game.

ASSISTANT COACH CONTRACT: Clubs now have the exclusive right to an assistant coach’s contract through the second Tuesday after their season has ended or last playoff game, rather than the third Tuesday as in the past.