Both local law enforcement and the airline refused to disclose details of what they call a "disturbance", but passengers told NBC the man claimed he had a bomb and attempted to gain access to the cockpit.
The plane, flying from Washington DC's Dulles Airport to Denver International, was forced to turn back "after a passenger failed to comply with crew instructions", a United spokesperson said.
The video, which has not been independently verified, appears to show the alleged would-be hijacker being held to the ground saying "I'm sorry! I'm sorry!" with blood on his face.
A picture from Reddit also appears to show two people holding a man on the ground in the aisle.
— Will (@BaddieWill) March 17, 2015
One of the flight's pilots told air traffic controllers "he ran forward towards the cockpit and he is being restrained by passengers," according to reports.
The incident occurred on board a Boeing 737 on Monday night, and passengers were accommodated on another flight early Tuesday morning. No passengers were injured and no weapons were found, according to an airport spokesperson.
The Metropolitan Washington Airports Authority and United Airlines have been approached for further comment.