If the man is interested in getting paid, he needs to sue both United and the law enforcement agency that removed him. Suing United won't yield much, and if United wanted to fight it all the way through litigation they could probably do so successfully - they didn't incapacitate him/bloody him, nor did they do anything they didn't have a legal right to do from what I can tell. It's probably worth the time and legal fees saved, though, to settle cheaply out of court.

The real payday will come from the folks that busted him up. I'm very empathetic to law enforcement - they had a man resisting arrest in tight quarters in an escalated situation. It could *easily* have turned into a riot on the plane if the other passengers sided with the man, so I have to give them some leeway. Still, it's hard for me to understand why a man needs to be bleeding from the mouth and apparently rendered unconscious to be removed. If other passenger's safety was a concern, tell the flight crew that you'll be happy to remove him as soon as they have all the other passengers disembark so that the safety issue is removed. If this was Chicago PD as I suspect it was, the odds of him being paid are even greater - they have a long history of excessive force claims against them to the tune of 8-figures or more over the past few years. This will likely go the same way. What works against him is the fact that they did have solid grounds to arrest him, and he resisted that arrest. Again, I'm not sure that justifies taking actions to make the man bleed from the mouth and render him unconscious, but I also wasn't there and haven't seen any video - only still shots.