One of the ugliest on-field incidents in NFL history Thursday night prompted one of its most stringent penalties Friday.

The league suspended Cleveland Browns defensive end Myles Garrett indefinitely for the episode late in Thursday’s game against the Pittsburgh Steelers in which Garrett yanked the helmet from the head of Steelers quarterback Mason Rudolph and hit him in the head with it.

Garrett’s suspension will cover at least the Browns’ six remaining games in the 2019 regular season and any postseason games they might play, the NFL said. He must meet with NFL Commissioner Roger Goodell or other league representatives before a decision is made about his reinstatement.

“Last night, I made a terrible mistake,” Garrett said in a statement released Friday by the Browns. “I lost my cool and what I did was selfish and unacceptable. I know that we are all responsible for our actions and I can only prove my true character through my actions moving forward. I want to apologize to Mason Rudolph, my teammates, our entire organization, our fans and to the NFL. I know I have to be accountable for what happened, learn from my mistake and I fully intend to do so.”

Garrett’s suspension, at a minimum of six games, already is the second-longest suspension for an on-field incident in league history. The NFL suspended Oakland Raiders linebacker Vontaze Burfict for the final 12 games of this season for an illegal hit, based on Burfict’s repeat-offender status. In 2006, defensive tackle Albert Haynesworth was suspended for five games for stomping on the head of Dallas Cowboys offensive lineman Andre Gurode after a play, requiring 30 stitches for Gurode.

The unsightly incident, which came in the final seconds of Cleveland’s nationally televised victory over Pittsburgh, was another black eye for the NFL in what is supposed to be a celebratory season commemorating its 100th anniversary. Instead, there have been controversies over officiating gaffes, the erratic behavior of wide receiver Antonio Brown during abbreviated stints with two teams and the audition that the league has organized Saturday in Atlanta for out-of-work quarterback Colin Kaepernick.

The NFL continues to thrive as a business and mainstay of American culture and remains, by far, the country’s most popular and prosperous sport. Television viewership is up for a second straight season, with audiences dwarfing those for other programming.

Yet there are growing concerns about the sport’s long-term viability amid issues about player safety and concussions. The NFL has taken steps toward improving player safety and reached a $1 billion settlement with players who sued over the effects of head injuries. Even so, there is anecdotal evidence of parents wary of allowing their kids to play football and reports of flagging participation in the sport at the youth and high school levels.

Against that backdrop, the Browns acknowledged after the game that they expected Garrett to be suspended and Garrett’s actions drew widespread scorn and condemnation by NFL players, analysts, former players and other observers. Former NFL quarterback Troy Aikman, an analyst on the Fox broadcast of the game, called the scene “barbaric.” Browns quarterback Baker Mayfield termed Garrett’s actions “inexcusable.”

Browns owners Jimmy and Dee Haslam also apologized Friday to Rudolph and said the team accepted the NFL’s penalties. “We are extremely disappointed in what transpired last evening at the end of our game,” the Haslams said in a statement. “There is no place for that in football and that is not reflective of the core values we strive for as an organization.”

Garrett can appeal his suspension, which is without pay. A six-game suspension would cost Garrett about $1.14 million of his 2019 salary of $3.23 million. The NFL said he also was fined an additional unspecified amount.

An appeal would be heard by either James Thrash or Derrick Brooks. Those two former NFL players are the appeals officers jointly appointed by the league and the NFL Players Association to resolve appeals of cases involving on-field discipline. That process generally moves quickly and is likely to be resolved before the Browns’ next game Nov. 24 against the Miami Dolphins in Cleveland.

“Garrett violated unnecessary roughness and unsportsmanlike conduct rules, as well as fighting, removing the helmet of an opponent and using the helmet as a weapon,” the NFL said in its announcement Friday.

In addition, the Steelers’ Maurkice Pouncey was suspended for three games and the Browns’ Larry Ogunjobi was suspended for one game for their roles in Thursday night’s melee between the teams. All the suspensions are without pay. The Browns and Steelers were fined $250,000 each.

Other players still could be fined by the league. There is likely to be a fine on Rudolph, who attempted to pull off Garrett’s helmet as the two wrestled on the ground.

Garrett is a standout player who has 10 quarterback sacks this season, tied for fourth-most in the league, and was the top overall selection in the 2017 NFL draft. He has a reputation for being soft-spoken and well-rounded off the field, with an interest in poetry and a fascination with dinosaurs. His charitable work includes a leadership role in the effort by former NFL player Chris Long’s foundation to supply clean water to needy communities in Africa.

“We support him in every way that you can, even if it’s an egregious mistake,” Browns coach Freddie Kitchens said in a conference call with reporters Friday. “We were expecting a response from the league. We accept their response.”

Garrett was fined by the NFL for several illegal hits earlier this season, including one that resulted in a season-ending ankle injury for New York Jets quarterback Trevor Siemian. Garrett told reporters Thursday night in the Browns’ locker room he had “made a mistake.”

“I lost my cool, and I regret it’s gonna come back to hurt our team,” Garrett said. “The guys who jumped into the scrum, I appreciate my team having my back. But it should never have gotten that far. It’s on me.”

The melee between the two teams started with eight seconds remaining in the Browns’ 21-7 triumph in Cleveland after Garrett hit Rudolph following a throw.

Rudolph attempted to pull Garrett’s helmet from his head as the two players wrestled on the turf. Garrett eventually pulled off Rudolph’s helmet and, with both players back on their feet and Garrett being pushed by Steelers guard David DeCastro, Garrett swung the helmet and it hit Rudolph’s unguarded head.

Rudolph said after the game he was “fine” and uninjured. He called Garrett’s actions “pretty cowardly, pretty bush league.”

Garrett, Ogunjobi and Pouncey were ejected from the game. Pouncey hit and kicked Garrett during the fracas. He told reporters in the Steelers’ locker room Thursday night that he was “in protection mode” and would accept any penalty given to him by the NFL. Pouncey also said that Garrett “absolutely, 100 percent” should be suspended for the remainder of the season.