TAMPA, Fla. -- Usually when flights are overbooked, airlines offer enough of an incentive to get people to voluntarily give up their seats.

But in the case that passengers are forced off the plane in voluntarily, what then?

Well, what happened to a man aboard Flight 3411 from Chicago to Louisville is going viral.

“That is ridiculous!” said Rosie Olle, a passenger at Tampa International Airport who had just seen the video taken by a passenger aboard flight 3411. And Rosie wasn’t alone in her assessment.

While we've all got our own nightmare travel stories, several people who have seen the images say it’s the worst they've seen. 

“Well, that is not cool. That is inhuman. Not good at all,” said passenger David Goto. “You don't drag somebody like that out of the plane.”

The video shows exactly that. A man, who claims to be a doctor, refusing to give up his seat involuntarily.

Airport security can be seen physically dragging the man from his row ad he screams. His head, say witnesses, appears to strike an armrest, and his mouth is bloodied. His glasses – knocked sideways, as his limp body is dragged down the aisle to the front of the plane.

"To be dragged out like that is horrifying,” said passenger Trisha Blake, watching the video.

We've all been there.

A flight is overbooked. A representative comes over the loud speaker and starts offering freebies, vouchers and other incentives to anyone who volunteers to get bumped. And for some, it’s a good deal.

“And, if you're not in a rush to get anywhere, why not?” said passenger Alex Jagiello.

But in this case, no one volunteered. United Airlines said it needed four seats to get its own employees to another flight.

So, they randomly selected the passengers and told them they had no choice. They had to get off the plane.

“If they are involuntarily bumped, they could be in for a pretty decent chunk of money,” said AAA Travel spokesman Mark Jenkins, who says passengers have rights whether they voluntarily or involuntarily give up their seats.

Jenkins points to Department of Transportation rules, which lay out compensation minimums for anyone involuntarily bumped from a flight.

Click here to see your rights under the Department of Transportation

If the airline gets you to where you were supposed to be within an hour of your scheduled arrival, you get nothing. But that jumps to 200% of the ticket value with a maximum of up to $675 if the delay is between one and two hours.

And it jumps to four times the fare, with a maximum of $1,350, if you get where you're going more than two hours later. Four hours internationally.

Legally, passengers are obligated to get off a plane if the airline demands it.

But attorneys who’ve see the viral video say that doesn’t give carriers the right to use excessive force. 

In this case, passengers we spoke with say to them it appeared to be unnecessary.

“It looks like he's passed out almost, too. It's insane,” said Jagiello.

“Oh my God, I can't believe that. Can you say lawsuit?” added Olle.

While an estimated about 50,000 passengers a year are bumped off flights involuntarily, usually it’s at the gate before passengers get on the plane, and rarely does it come to this.

United Airlines said in a posted statement: “This is an upsetting event to all of us here at United. I apologize for having to re-accommodate these customers. Our team is moving with a sense of urgency to work with the authorities and conduct our own detailed review of what happened. We are also reaching out to this passenger to talk directly to him and further address and resolve this situation."