This Little Gadget Caused an Epic Airline Passenger Brawl A United Airlines flight was diverted after using something banned by most airlines: an anti-reclining seat device called the Knee Defender.

Flying domestic? OK good, get ready to smush yourself into a cramped, uncomfortable seat for the duration of the flight. And that's not just my humble opinion: I have research on my side, research that confirms American airline seats are the most uncomfortable seats in the world.

It's extra bad, then, when the person in front of you on a flight decides to take away the one comfort you have left – some semblance of legroom – with the fell recline of his or her seat.

Sensing an opportunity, a company named Gadget Duck created a provocative device that allows travelers to reclaim their legroom. Called the Knee Defender, it consists of key-sized plastic claws that latch onto the arms of your tray table, thus preventing the passenger in front of you from reclining his or her seat.

Related: This In-Flight Gadget Prevents Pushy Passengers From Reclining Their Seats

Sound controversial? That's because the Knee Defender most certainly is -- controversial enough, in fact, that it sparked an in-flight fight between two frustrated passengers and diverted an entire plane.

The showdown occurred this Sunday, according to the Associated Press, when a man on his laptop in row 12 of a United Airlines flight from Newark, N.J., to Denver, Colo., rebuffed a stewardess' request to unclamp his Knee Defender and allow the women in front of him to recline her seat.

The woman in front of him was having none of it: According to a law official, she promptly got up and threw a cup of water at the man and his laptop. Things escalated enough from there that the plane was diverted to Chicago's O'Hare international airport, where both passengers were questioned by local police.

Related: Traveling Coach on U.S. Flights Has Become a Serious Pain

While the Knee Defender is not banned by the Federal Aviation Administration – the agency allows individual airlines to implement rules regarding the clamp -- most airlines have issued a blanket ban on the device, including United Airlines.

Perhaps this could have all been avoided if the man in row 12 had simply handed the women in front of him a "Courtesy Card," available for print and download on the Gadget Duck website, which reads: "I realize that this may be an inconvenience. If so, I hope you will complain to the airline. Maybe working together we can convince the airlines to provide enough space between rows."

…Or on second thought, perhaps not.

Related: British Airways Testing 'Happiness Blanket' to Make First-Class More Comfortable