A United Airlines flight from Newark to Denver was diverted because of two passengers who were fighting over a little bit of legroom.

A woman and a man — both seated in the “Economy Plus” section of the aircraft, which already comes with extra legroom — were at each other’s throats because the man attached a “knee defender” device to his seat, preventing the woman in front from reclining, according the Associated Press.

The $22 device locks onto the tray table on the back of the seat, making it impossible for the person in front to recline during the flight. United Airlines and other U.S. carriers have banned the device. The Federal Aviation Administration says it can’t be used during taxi, takeoff and landings, when tray tables and reclined seats aren’t supposed to be in use anyway.

United flight attendants asked the man to remove the device on the Sunday flight, but he refused.

Things were so bad that the female passenger threw a cup of water at the man, according to the AP. At that point, the pilot diverted Flight 1462 to Chicago’s O’Hare International Airport

Both passengers were removed from the flight and the remaining passengers continued on their trip to Denver. No arrests were made.

Over the years, seats have been getting more uncomfortable and legroom more scarce — unless, of course, you’re willing to pay.

More than a decade ago, 6-foot-3 Ira Goldman invented the “knee defender” to protect his “right” to legroom. At the time, Goldman, a former Capitol Hill staff member, told The Washington Post that the device wasn’t about “space” — it was about “protection.”

But as The Post noted presciently in 2003: “It’s a recipe for air rage.”

Have you ever been in a dispute over space on an airplane? Let us know in the comments below.