From Freakonomics Blog: Airplane Seat Reclining: A Good Real-World Altruism Test? Quoting WaPo:

Before things got out of hand, it was a typical annoyance that happens once a flight gets airborne: A passenger hit the recline button and sent his seat intimately close to the lap of the guy sitting behind him.
What followed wasn’t typical at all: a smack to the head, peacemakers diving about the cabin to intervene and a pair of Air Force F-16 fighter jets scrambling into the night skies over Washington.
It happened late Sunday, just after a United Airlines Boeing 767 bound for Ghana with 144 passengers took off from Dulles International Airport.
Not long after the 10:44 p.m. departure for the overnight flight, the offending seat was lowered into the offended lap, and a fight ensued. A flight attendant and another passenger jumped in between, said sources familiar with the incident who spoke on the condition of anonymity because they were not authorized to provide details.
The pilot has complete authority over the aircraft, a United spokesman said, and he decided to return to Dulles to sort things out rather than continue the transatlantic flight to Ghana when he was unsure of the scope of the problem.

My sympathies with the smacker.