The US carrier United Airlines says a man wouldn't give up his spot on an overbooked flight Sunday.

So, according to witnesses and videos of the incident, he was pulled screaming from his seat by security, knocked against an arm rest and dragged down the aisle and back to the terminal at Chicago's O'Hare International Airport.

United refused to answer questions about the incident, which horrified other passengers on the Louisville-bound flight. A United spokesman only confirmed that the flight was overbooked, a passenger "refused to leave the aircraft voluntarily," and United called police.

What followed was captured on mobile phone video by at least two passengers.