How Emmitt Smith, Joe Horn, Tom Brady and more altered NFL rule book

Hoodies, assistant coaches no longer allowed on NFL field (1:44)

Dan Graziano breaks down the NFL rule adjustments made this offseason, including players wearing hoodies and assistant coaches on the playing field during games. (1:44)

The structure of football in the NFL dates back more than 100 years. The rest of the league's 79-page rule book? Much of it is the result of outlawed innovation bubbled up from competitive-minded teams and players.

The latest manifestation of that practice occurred last week, when it was revealed the NFL has banned the New England Patriots' preference of using numberless jerseys during spring practices. That news arrived a few days after the league addressed a series of 2015 issues with rule clarifications, most notably prohibiting exposed sweatshirt hoodies worn by free-agent receiver James Jones.

As former commissioner Paul Tagliabue once said as he tried to bar "poison pill" clauses in free-agent contracts: "The minds of creative people know no limit." And it got us thinking. (Dangerous, I know.)

How many of the NFL rules that we know (and love) were prompted by a single or small group of events? Let's consider 15 instances when the NFL felt compelled to rein in the minds of creative people -- more than occasionally with good reason.

Consider this a sample -- a member of the Pro Football Researchers Association delivered an entire paper on it!

Practice jerseys

Rule: All participating players must wear jerseys with numbers on them during Phase 3 of the offseason program.

Source: The Patriots, following an example set by former Pittsburgh Steelers coach Chuck Noll, among others. Coach Bill Belichick believes blank jerseys force better communication and foster more bonding among teammates.

Reasoning: Without numbers, the NFL can't perform random compliance checks of other rules via practice video. Among the violations investigators scan for: participation by injured players, who can be identified by their numbers.

Ineligible players with eligible numbers

Rule: It is illegal substitution for an offensive player wearing an eligible number -- 1-49 or 80-89 -- to report as ineligible and line up outside the tackle box.

Source: The Patriots used that strategy on three plays in the 2014 playoffs, surprising the Baltimore Ravens and scoring a quick touchdown after halftime.

Reasoning: The NFL legislates against any attempt to manipulate rules into a competitive advantage. Of course, the league can't outlaw something until someone thinks of it -- and puts it into play -- first.

The Tom Brady rule

Rule: A defender on the ground, who hasn't been pushed into the quarterback, can't lunge at a quarterback's legs at the knee or lower. This strengthened an existing rule.

Source: Brady suffered two torn ligaments in 2008 during the Patriots' season-opening game against the Kansas City Chiefs. Safety Bernard Pollard was blocked to the ground but then dove for Brady's knee in an attempt to sack him.

Reasoning: The NFL added the rule after that season as part of its ongoing efforts to give quarterbacks special protection in the pocket, where the stars of the game are at their most vulnerable.

Hooded sweatshirts

Rule: Exposed hoodies are a violation of the uniform policy.

Source: Jones, who played last season for the Green Bay Packers, said he wore the hoodie "just to stay warm" during a Nov. 22 game and then continued because he hoped it was a good-luck charm.

Reasoning: The hood blocked Jones' nameplate on the back of his jersey, but the NFL has not publicized its full explanation. Best guess: The uniform policy is designed to, well, keep everyone uniform. It's no different than the requirement that all teammates wear the same shoe color.

Coaches on the field

Rule: Only head coaches are allowed on the field of play during a game, and even then only to check on injured players.

Source: Steelers assistant Joey Porter wandered onto the field during a wild-card playoff game in January as receiver Antonio Brown was being evaluated for a head injury. Porter wound up in a shouting and pushing match with Cincinnati Bengals players and provoked a 15-yard penalty from cornerback Adam Jones.

Reasoning: The rule had always been implied but had not been codified. Porter was not penalized, so putting the policy in writing allows officials to enforce it now without question.

The coin toss

Rule: If the coin does not flip during the pregame (or pre-overtime) toss, the referee must repeat the toss. The captain's original call stands.

Source: Wouldn't you know it? A coin actually failed to flip prior to overtime of last season's divisional playoff game between the Packers and Arizona Cardinals.

Reasoning: There was no applicable language in the rule book to fall back on. Referee Clete Blakeman made his own judgment to re-flip, and his response is now codified for future use.

Horse-collar tackles

Rule: Players can't grab the inside collar from the back or the side of shoulder pads and attempt to pull a ball carrier to the ground. (The rule was expanded in 2016 to include the nameplate area.)

Source: In 2004, Dallas Cowboys safety Roy Williams caused multiple injuries -- most notably to Philadelphia Eagles receiver Terrell Owens -- after pulling players by the collar from behind. Owens suffered a broken leg. These specific type of tackles were legal at the time.

Reasoning: The action puts runners in an awkward position, especially if a foot or feet remain planted in the ground as they are pulled backward.

Holy Roller

Rule: A fumble in the final two minutes of a half can be recovered by anyone, but it can only be advanced by the player who fumbled it (or a member of the opposing team). The ball is dead at the moment of recovery by a teammate.

Source: In 1978, Oakland Raiders quarterback Ken Stabler fumbled while avoiding a sack as his team trailed the San Diego Chargers 20-14. Raiders running back Pete Banaszak, unable to recover, pushed the ball toward the goal line. Raiders tight end Dave Casper did the same before ultimately recovering for the game-winning touchdown.

Reasoning: Stabler admitted he fumbled on purpose, and it wasn't difficult to figure out the intentions of Banaszak or Casper. The NFL added the Holy Roller rule the following offseason, hoping to close the loophole on intentional fumbles and prevent what amounts to a forward pass beyond the line of scrimmage.

Celebrating on the ground

Rule: It is unsportsmanlike conduct for a player to celebrate while on the ground.

Source: In 2005, Bengals receiver Chad Johnson dropped to one knee after scoring a touchdown and "proposed" to a cheerleader. It was one of several over-the-top celebrations in the years leading up to it, including New Orleans Saints receiver Joe Horn using a cell phone hidden underneath a goal post in 2003 and Owens performing situps in 2004.

Reasoning: The NFL wanted to minimize instances of celebrations provoking altercations. Rules against going to the ground, and using props such as Horn's cell phone, were its attempt to draw the line between celebrations and taunting.

The Bronko Nagurski Rule

Rule: Passes can be thrown from anywhere behind the line of scrimmage.

Source: In 1932, all passes were required to be thrown from at least 5 yards behind the line of scrimmage. In a playoff game, Nagurski faked a run into the line of scrimmage, took a step back and lobbed the ball to Red Grange as part of the Chicago Bears' 9-0 victory over the Portsmouth Spartans.

Reasoning: The Spartans complained that Nagurski was less than 5 yards behind the line, but no penalty was called. In the end, league officials loved the new dimension it provided. Football historians consider it the birth of the passing game as we know it.

The Emmitt Smith Rule

Rule: It is unsportsmanlike conduct for a player to remove his helmet on the field during a touchdown celebration or confrontation.

Source: Smith, the Cowboys' eventual Hall of Fame running back, routinely took off his helmet in such situations. By 1997, Smith's eighth season, the NFL had outlawed it.

Reasoning: The league considered it taunting, an act it hoped to minimize for sportsmanship reasons and for the potential consequence of further post-play confrontation.

The Hines Ward Rule

Rule: It is illegal to block a defender from the blindside at the head or neck area with the blocker's head/shoulder or forearm.

Source: Ward's block on Bengals linebacker Keith Rivers in 2008 while playing for the Steelers. The hit broke Rivers' jaw. The NFL updated the rule for the 2009 season.

Reasoning: Rivers did not see Ward coming and could not brace himself for the hit. The NFL created its growing category of "defenseless posture" for these situations: protecting obvious instances where they are at a safety disadvantage.

The Tom Dempsey Rule

Rule: Any shoe worn by a player with an artificial limb on his kicking leg must have a kicking surface that conforms to that of a normal kicking shoe.

Source: That sounds awfully specific, and it is. Dempsey, born in 1947 without toes on his right foot, wore a customized shoe with a flat edge. He kicked a 63-yard field goal in 1970 for the Saints, a league record that stood for 43 years, and went on to kick in the NFL until 1979.

Reasoning: The rule, adopted in 1977, was part of a league effort to make field goals more difficult. It sought to wipe out any advantage that Dempsey, or any future kicker, might receive from shoe design.

The Jim Schwartz Rule

Rule: The penalty for challenging either a non-reviewable or automatically reviewed play is a lost timeout. If the team has no timeouts remaining, it will receive a 15-yard penalty.

Source: Schwartz, at the time the Detroit Lions' coach, challenged a touchdown scored by Houston Texans tailback Justin Forsett during a game in 2012. Forsett appeared to be down by contact before scoring.

Reasoning: At the time, an illegal challenge was considered a delay of game, making it a non-reviewable play. Had Schwartz not challenged, referee Walt Coleman would have automatically reviewed the score and almost certainly reversed it. The NFL considered the consequence too severe for the level of foul Schwartz committed.

The Boise State Rule

Rule: The entire field of play must be a league-approved shade of green.

Source: You might not think it needed to be addressed, but in recent years, corporate sponsors had approached teams about adjusting field colors as part of campaigns.

Reasoning: The field used by Boise State University is a well-known shade of blue, which, as legend has it, causes birds to mistake it for water. The NFL's policy for playing surfaces is similar to its uniform policy. It wants all fields to have a standard appearance.