Flight Diverted After Passengers Feud Over ‘Knee Defender’ Blocking Reclining Seat A passenger used the "Knee Defender" to prevent a reclining seat.

 -- A $22 product designed to protect the most sacred of things when flying –- personal space -– led to an unscheduled landing in Chicago during a flight from Newark to Denver.

Two passengers aboard the diverted United Airlines flight got into a heated argument Sunday after a male passenger used the product, the Knee Defender, to prevent the woman in the row in front from reclining her seat.

The man, who was not identified, placed the Knee Defender’s brackets on his tray table attached to the back of the seat in front of him, 11B.

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The female passenger seated in 11B became angry over not being able to recline her seat and reportedly threw a cup of water in the man’s face.

Both passengers were seated in United’s Economy Plus section, which gives you extra legroom for an extra fee.

A United Airlines spokesperson confirmed to ABC News the flight was diverted due to the argument and that both passengers were removed from the plane and not allowed to reboard when the plane continued to Denver.

Neither of the passengers was arrested, airport and law enforcement officials with knowledge of the incident confirmed to ABC News.

The man who invented the Knee Defender, Ira Goldman, says that he created the device for exactly the opposite reason of what happened on the United flight.

"Knee Defenders aren't about getting more space," Goldman told ABC News. "They're about stopping something from moving and hitting you."

"It starts the conversation before there's a problem," he said. "This has been on a market for 11 years next month. [It’s] never happened before."