A man is under arrest and under investigation by the FBI after an inflight incident on a Dulles-bound flight out of SFO Monday in which the man allegedly pummeled another man who was sleeping for no known reason.The incident happened on United Flight 2247 from SFO to Washington Dulles Airport in eastern Virginia aroud 12:30 pm Monday. As KTVU reports, 44-year-old Everett Chad Nelson allegedly got up from his seat in the rear of the plane about two hours into the flight ostensibly to use the lavatory. Nelson then allegedly stopped at seat 12F — which would be a window seat — and began punching a sleeping man in the face, drawing blood."He was just very violently and very aggressively just pummeling the guy who was in the window seat who was in front of me and it was vicious," says witness Sandhya Gupta, speaking to ABC 7. "This wasn't like a bar room, I'm going to throw a couple of punches around, I mean this was vicious."Gupta adds that she heard "blood-curdling screams" from the victim, who turned out to be deaf and non-verbal. The assault reportedly went on until another passenger intervened and pulled Nelson off of the victim, after which, Gupta says, Nelson "went limp." Nelson was then escorted to another area of the plane where this other passenger continued to monitor him until they landed.In the aftermath of the assault, a doctor onboard apparently tried to help the victim, who was communicating with flight attendants and the doctor using text messages on his phone. "This doctor was just like trying to stop the bleeding, his face was just a mess. It was awful," Gupta tells ABC 7. "There was blood spatter on the window shape and all that kind of stuff."An FBI affadavit suggests that the assailant and victim did not know each other, and the victim reportedly said this to flight attendants via a text message. A witness suggested that Nelson was saying that the victim had attacked him in the street earlier.The affadavit notes that blood splatter could be seen on Nelson's lime-green windbreaker.A United spokesperson tells KTVU that it was "thanks to the quick action of our crew and customers" that Nelson was restrained. The flight landed safely at Dulles, and Nelson was taken into federal custody. A trial date has reportedly already been set for December 11.The FAA is also investigating the incident.While reports of unruly passengers and assaults — particularly inflicted on flight attendants — hit an all-time high during the pandemic, in 2021, such reports have since dropped by about 80%. According to the FAA, airlines have reported over 1,240 unruly passenger cases so far in 2024.Related: Woman Shouting Threats and Profanities at Flight Attendant Causes Alaska Flight Out of SFO to Be Diverted