An aviation attorney has weighed in from the article linked here:
David Dao vs United Lawsuit - How Much Can United Airlines Be Sued For
"First, Wolk believes the airline breached its own contract by removing Dao. Having read United's contract of carriage in its entirety, Wolk thinks Dao could sue for assault and battery, intentional infliction of emotional disturbance, and may also have grounds to sue under various civil rights acts, in addition to that breach of contract.
"There is nothing in that contract that gives United the right to commit an assault and battery on a passenger," he told me over the phone.
"This is not a denied boarding incident, which is covered by the contract; this man was already boarded. This is not an oversold incident, as provided for by the contract; this airplane was not oversold—every passenger was ticketed and had a seat.
"This was not a situation where the passenger was unruly, committed a criminal act, interfered with the flight crew, was incapable of being a passenger by himself or anything of that nature, obviously until they attempted to physically throw him off the airplane.
"So to me, United Airlines breached their own contract of carriage."
Second, if Wolk points out that if this case does go to trial, the case would come down to the jury—another major obstacle for United. "You have to understand what your jury pool is going to look like here. Virtually every person who has flown on an airline flight on a regular basis feels that airlines abuse their passengers. The mindset of the jury pool is that they hate the way they're being treated by airlines."