Federal prosecutors said Brian Hsu has been charged with assault and interference with a flight crew.
US Magistrate Judge Autumn Spaeth set Hsu's bond at $10,000 during an initial court appearance on Monday.
Flight 976 from John F. Kennedy International Airport in New York City to Santa Ana, California, was diverted to Denver after the incident last week.
According to an FBI affidavit, part of a criminal complaint filed Friday, the flight attendant told investigators the confrontation began when a male passenger approached her as she stood in the mid-galley section of the plane when, she said, she felt something strike her in the head.
When she turned to see what had struck her, she saw a male passenger and asked if he was all right. The flight attendant told the FBI that he did not apologize and instead just stated that he needed to use the bathroom. The flight attendant told the man the bathroom was occupied and he would need to wait in his seat because the "fasten seatbelt" sign was on, the affidavit says.
"The Victim advised that the male passenger raised his arms as though he were going to stretch, but then brought his elbow down and struck the Victim on the head," the affidavit says.
Investigators said the flight attendant told them she then took a defensive position and the passenger initially backed down, "but then charged at her, flailing his arms."
"This caught the attention of another flight attendant, who came to assist. The male passenger backed down again, but when he charged at the Victim this time, he struck her in the face with the closed fist of his right hand," the affidavit says.
According to a witness interviewed by the FBI, the man struck the flight attendant with a "full swing," the complaint says.
The flight attendant "advised that her nose was bleeding and she felt dizzy and nauseous," the criminal complaint says.
Crew members and passengers subsequently restrained the passenger in his seat using duct tape and plastic bonds, the complaint says.
Hsu was interviewed by an FBI agent after being removed from the plane in Denver, according to court documents. He told the agent he was returning to California after undergoing brain surgery to address injuries sustained after being assaulted in New York in 2020.
"HSU reported psychological damage from the injury, including ringing in his ears, nausea, dizziness, and loss of balance. He also stated that he is now sensitive to sound and sometimes experiences a mental 'fog,' during which thinking is difficult," the FBI's affidavit says.
He also claimed he was defending himself from the flight attendant who he said became agitated after he accidentally bumped her, according to the affidavit. Hsu allegedly told investigators "that the Victim charged at him and hit her nose against the palm of his right hand," and that "he became scared because an impact to his head in its current state could cause severe injury or even death."
Hsu also said a recent injury to his right hand meant he could not have clenched it to make a fist.
The flight attendant was taken to a Denver hospital and told investigators she had a concussion but doctors were unable to determine whether her nose was fractured because of swelling, the criminal complaint says.
Airline chief wants suspect prosecuted 'to the fullest extent possible'
The head of American Airlines said last week the incident "is one of the worst displays of unruly behavior we've ever witnessed."
In a video statement posted on social media, American Airlines CEO Doug Parker said the airline was supporting the injured flight attendant and banning the man accused of assaulting her from flying on the airline again.
"That is not enough," said Parker. "We're doing everything we can to ensure he is prosecuted to the fullest extent possible."
The Federal Aviation Administration (FAA) said Thursday that it would investigate the incident.
Following the reported attack, Transportation Secretary Pete Buttigieg said a federal no-fly list for violent airplane passengers "should be on the table."
"It is completely unacceptable to mistreat, abuse or even disrespect flight crews," Buttigieg told CNN's Dana Bash on "State of the Union" Sunday, adding, "We will continue to look at all options to make sure that flight crews and passengers are safe."
"There is absolutely no excuse for this kind of treatment of flight crews in the air or any of the essential workers -- from bus drivers to air crews who get people to where they need to be," he said.
The FAA adopted a zero-tolerance policy for unruly passengers on board flights earlier this year. The agency said in August it had issued more than $1 million in fines to unruly passengers in 2021. In its latest update, the FAA said there had been 4,941 unruly passenger reports this year.