The NFL is poised to discipline Cleveland Browns defensive end Myles Garrett, who ignited an on-field fight Thursday night when he yanked Pittsburgh Steelers quarterback Mason Rudolph's helmet off and whacked him in the head with it.

Garrett's actions obliterated the NFL's boundaries of controlled violence, resulting in his immediate expulsion from the game. The brawling triggered shock and outrage and disbelief in the closing seconds of a game that that his defense had dominated.

It's widely expected that Garrett will be hit with a lengthy suspension for breaking an assortment of the NFL's most serious rules, from egregiously roughing the quarterback and fighting to striking someone in the head. The league has not yet responded to NPR's request for comment.

Garrett was ejected from the game along with Steelers' offensive linemen David DeCastro and Maurkice Pouncey, who rushed in and took Garrett to the ground in retaliation for his attack on Rudolph. As DeCastro grappled with Garrett, Pouncey punched and kicked at his helmet.

Discussing the fracas after the game, Garrett said it was "embarrassing and foolish and a bad representation of who we want to be."

"Rivalry or not, we can't do that. We're endangering the other team. It's inexcusable," Browns quarterback Baker Mayfield said.

The NFL has a personal safety rule forbidding "impermissible use of the helmet" — but the rulebook foresaw players using their own helmet to hit others in the course of a game, not a football player ripping an opponent's helmet off and striking him with it.

"I made a mistake, I lost my cool," Garrett said afterward. "And I regret it. It's going to come back to hurt our team. The guys who jumped in the little scrum — I appreciate my team having my back, but it should never have gotten to that point. That's on me."

"I thought it was pretty cowardly, pretty bush league," Rudolph said after the game. When asked how he was feeling after the violent end to a tough game, he replied, "I'm fine. I'm good, good to go."

Former Steelers linebacker James Harrison — who faced his own suspensions for dangerous hits during his career, was one of many NFL insiders who said Garrett's actions amounted to assault.

"That's assault at the least," Harrison said via Twitter. He added, "6 months in jail on the street.. now add the weapon and that's at least a year right?!"

The incident began with around 10 seconds left in the game: Garrett grabbed Rudolph as the quarterback completed a harmless third-down pass in the Steelers' own end, stopping the game clock at 8 seconds. But after Garrett tugged and twisted Rudolph to the ground, the two began wrestling and Rudolph grasped Garrett's helmet with both hands.

As they got up, Garrett ripped the quarterback's helmet off by its facemask — and as DeCastro tried to intervene, Garrett swung Rudolph's helmet in a vicious overhand arc, hitting the quarterback. As Rudolph turned to an official seeking a penalty, the Browns' Larry Ogunjobi leveled him from behind, sending him back down to the turf.

At the time, the Browns were leading 21-7, and their defense had already recorded four sacks and four interceptions against Rudolph's Steelers. In the Browns' stat sheet for the night, Garrett was notably absent from its sack list.

Going into Thursday night's game, Garrett was leading the AFC in sacks, with 10 quarterback takedowns through the first nine games of the season. He had also been effective against the Steelers, recording four sacks and forcing three fumbles in just three games against the Browns' division rivals.

Cleveland started the year on a wave of optimism, with talk of a possible run deep into the playoffs. But the team hasn't lived up to those expectations. And now — instead of discussing their hopes to build on a win that brought their record to 4-6 — the Browns and Garrett are the talk of the NFL for all the worst reasons.

Prior to Garrett's ejection, Browns safety Damarious Randall was also kicked out of Thursday night's game, for delivering a dangerous helmet-to-helmet hit on Steelers wide receiver Diontae Johnson. But it was the end of the game that left the worst impressions in Cleveland.

"It feels like we lost," Mayfield said afterward.

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