The passenger was arrested in relation to the incident, despite claiming that the employee "assaulted" him and threw the first punch in the video, law enforcement confirmed to TMZ.
The video was initially shared by Twitter user @DMNTnasa just before 9:00 a.m. on Sunday (May 22) and shows the United employee slap the passenger, who asks, "you saw that s***?" before landing a punch that forces the employee to stumble backward over the counter as the passenger lands more punches.
The employee stands back up and has a large, bloody gash near his left eye as he attempts to walk back to the passenger, who then asks, "you want some more?"
Witnesses at the airport told TMZ that the two men were arguing, pushing and slapping before the fight escalated.
Multiple Twitter users attempted to identify themselves as the passenger in the video.
Singer-songwriter Larren Wong claimed he was the man in the video, quote-tweeting the original post with "Security had me bent glad someone caught this on film."
Twitter user @Trllang claimed he was the man in the video and called Wong a "struggling artist" who would "do anything for pennies" in response to the singer's claim.