Man accused of "one of the worst displays of unruly behavior we've ever witnessed" pleads not guilty to punching American Airlines attendant

Brian Hsu (20) of Irvine, California was banned from American Airlines for allegedy assaulting a crew member, giving her a concussion and broken facial bones. Hsu, who was flying first class at the time, was also formally charged with criminal interference with a flight crew and assault, to which he is pleading not guilty.

American Airlines' CEO called the attack "one of the worst displays of unruly behavior we've ever witnessed."

From the Denver CBS news affiliate:

The incident happened when the flight attendant says she told him he could not use the lavatory.

Hsu claims the flight attendant then charged at him. One court document says Hsu indicated he had brain surgery in Rhode Island just one month before that flight.

Another says, "Hsu stated that he became scared because an impact to his head in its current state could cause him severe injury or death."

The FBI wrote Hsu told them in an interview he was playing football during the time between the brain surgery and the flight.

Hsu is free on bond. He faces up to 20 years in prison if found guilty.