The Irvine, CA man who allegedly punched a flight attendant repeatedly on an American Airlines flight last week claims his actions were in “self-defense.”

According to the Dallas Morning News, the assaulter, Brian Hsu, was returning home from brain surgery in Rhode Island. The Association of Professional Flight Attendants union says that the attendant was punched twice in the face and suffered multiple fractures, including a broken nose.

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Twenty-year-old Hsu says he was assaulted in New York last year and received surgery to repair parts of his skull. When speaking with the FBI, Hsu claims the surgery left him in a “mental fog,” and his temper became shorter.

On the plane back from Rhode Island, Hsu was reportedly “pacing an unusual amount” throughout the aisles. Flight attendants said that Hsu was asked to take a seat when the plane caught turbulence, and allegedly then he struck the flight attendant. Hsu allegedly hit the attendant another time after “backing off.”

Hsu’s attorney claimed self-defense based on Hsu’s fragile status on the flight. Court documents show that Hsu believed the flight attendant was “flailing her arms” near his head, which could have caused him further injury. A witness on the flight said that the attendant did make a jumping motion towards Hsu. Other witnesses described Hsu’s assault as being brutal, almost as though he was “trained.”

The passenger has been banned from flying with American Airlines, and the attendant and airline company intend to take legal action. Doug Parker, CEO of American Airlines, stated that the attack was “one of the worst displays of unruly behavior we’ve ever witnessed.” Flight unions have begun to call upon the FAA to implement an encompassing no-fly list, which would bar travelers such as Hsu from flying on any airline.