The Cincinnati Bengals and Pittsburgh Steelers have become one of the most heated rivalries in the NFL over the past decade, and for good reason.

The Bengals-Steelers matchups have become knockdown, drag-out fights each time they play. There have been as many flags, penalties and fines lately as there have been brutal hits.

But the repercussions of the rivalry have extended beyond the AFC North division. It has actually changed the NFL, too.

A number of rule changes have been made in the past decade as a direct or indirect result of something that happened in a Bengals-Steelers game.

The NFL changed a rule concerning defensive players using the crown of their helmet -- no matter the angle they take -- after Ryan Shazier gave Giovani Bernard a concussion on this play in the AFC playoffs last season. Aaron Doster/USA Today Sports

Here’s a list of the rule changes, clarifications and reminders, and why they occurred:

2006 season: The "Carson Palmer rule"

It’s a common misconception that Patriots quarterback Tom Brady was the reason the NFL changed the rules to protect quarterbacks' knees. In fact, one of those rules is often referred to as the “Tom Brady rule.”

True, the NFL clarified the language in 2009 of part of the rule after Brady went down with a torn ACL at the beginning of the 2008 season. The injury came after Chiefs safety Bernard Pollard dove at Brady's left knee.

However, that rule was once informally called the “Carson Palmer rule.”

Palmer, then with the Bengals, was only a few plays into the AFC wild-card game in January 2006, when Steelers defensive end Kimo von Oelhoffen rolled into his left leg after Palmer completed a pass to Chris Henry. Palmer suffered a gruesome knee injury that ended his season and the Bengals’ hopes of a playoff win.

Quarterback knee injuries were somewhat in the spotlight that season after Ben Roethlisberger and Brian Griese also injured their knees (Roethlisberger came back, but Griese tore his ACL and was out for the season).

During the 2006 offseason, the NFL's competition committee proposed a rule change to make the game safer for quarterbacks.

The rule read: “A rushing defender is prohibited from forcibly hitting in the knee area or below a passer who has one or both feet on the ground, even if the initial contact is above the knee. It is not a foul if the defender is blocked (or fouled) into the passer and has no opportunity to avoid him.”

Thus the “Tom Brady rule” would be better termed the “Tom Brady clarification.”

During the 2008 NFL owners meetings, the league added a provision to the rule that would penalize defenders who had been blocked into the ground from lunging at a quarterback’s knees, even if the play was still ongoing.

2009 season: The "Hines Ward rule"

Steelers wide receiver Hines Ward once ended the 2008 season of linebacker Keith Rivers when he broke his jaw after a physical blindside block.

Rivers never saw Ward coming. Ward had a reputation for being a dirty player. One year after the block, his peers anonymously named him the "dirtiest player in the NFL" in a Sports Illustrated poll.

However, the hit on Rivers was perfectly legal at the time. It would draw a 15-yard penalty today.

The NFL passed a rule change in the 2009 offseason that made blindside blocks illegal if the blocker's helmet, shoulder or forearm made contact with the head or neck area of the opponent, who is considered a defenseless player in that situation. The Steelers were the only team to vote against the rule.

Ward's hit on Rivers was used in an informational video by officials highlighting the new rule changes for the 2009 season.

2013 season: NFL admits mistake after Kevin Huber breaks jaw

The NFL didn't make any rule changes after a violent hit by Steelers linebacker Terence Garvin broke the jaw and neck of Bengals punter Kevin Huber. Steelers receiver Antonio Brown returned the punt for a touchdown.

Huber had moved toward Brown on the play as if to make a tackle when Garvin delivered a blow to Huber's jaw from the side.

There weren't changes, but the NFL admitted the officials made a mistake when they didn't penalize the play when it happened. The NFL reminded officials the following week that punters and kickers are considered defenseless players throughout the down.

2016 season: The "Joey Porter rule" and clarifications on helmet-to-helmet hits

The Bengals likely won't be getting into any more verbal altercations with Steelers assistant coaches. Under a new rule, only head coaches are allowed on the field to check on injured players.

Dubbed the "Joey Porter rule" after the Steelers assistant coach, the rule was enacted after the chaotic ending to the Steelers-Bengals AFC wild-card playoff game last season. Porter was fined $10,000 for his part in an altercation with Bengals cornerback Adam Jones toward the end of the game, but did not draw a flag under the rules at that time. Jones was flagged for unsportsmanlike conduct, helping the Steelers move into position to set up a game-winning field goal.

The league also announced changes in the interpretation of a helmet-to-helmet hit after Steelers linebacker Ryan Shazier gave Bengals running back Giovani Bernard a concussion. Bernard was knocked unconscious and lost the football as a result of the play, which almost prompted a skirmish between his fellow running back, Jeremy Hill, and Steelers defenders.

The NFL said Shazier wasn't flagged because Bernard had turned and established himself as a runner instead of a defenseless receiver. Additionally, Shazier didn't intentionally line up "head on" with Bernard.

That won't matter in 2016.

With the clarification, defensive players can no longer use the crown of their helmet outside of the tackle box, no matter what angle they take. The NFL said the change is to discourage defenders from leading with the crown of their helmet.