Transcript for United Airlines passenger apparently dragged off flight after refusing to give up seat
We turn to the chaotic scene unfolding on a united flight in Chicago. Initially passengers were told the flight was overbooked. Four passengers were told to get off. One of the passengers was dragged down the aisle and off the plane bleeding from the struggle. He did not want to give up his seat. Tonight the airline's exblow nation. We ask, what are your rights once you board the plane? ABC's David Kerley covers aviation. Ow. Reporter: It is a stunning scene. That passenger, yanked from his row. Oh, my god. Reporter: Lip cut, dragged off a united jet, refusing to give up his paid seat. My gosh. Reporter: Tonight, an aviation security officer involved here, put on leave. But so many are asking, how could this have happened? John Klassen in the Orange shirt, saw and heard it all. After having done really nothing other than this is my seat, I've bought and paid for it. I need to go to Louisville. I could not believe what I was seeing or hearing, I was in shock. Reporter: United airlines told passengers the flight was overbooked. It now says it was a crew transport issue, four seats needed to get a crew from Chicago to Louisville. $800 in vouchers offered, no takers. So, a united's computer picked four passengers, including the 69-year-old man who said he's a doctor, saying he had to get home to treat patients. The man slipped back on the jet. I need to go home. I need to go home. Reporter: Before he was removed again. United's CEO calls it an upsetting event. Apologizes for having to reaccommodate these passengers. But no direct apology to the man. The overbooking, even demanding a paying customer give up a seat, is perfectly legal. It's part of a document that nobody ever looks at called the contract of carriage which basically gives the airline, the pilots the flight attendants all sorts of rights to do pretty much whatever they want. All right, David Kerley live with us tonight. You reported there it's in the fine print part of the contract in the ticket. They can order you to get off even when you're on the plane. But passengers do have right. They're due compensation if they get bumped from the plane. A lot of people weighing in on this one today. David Kerley thank you.
This transcript has been automatically generated and may not be 100% accurate.