I have only experienced one episode of (mild) violence on a plane and sorry to say I was a participant... I was flying to France to do some research at Saclay, the plane was half empty, I had the entire middle row to myself, behind me was a VERY inebriated older Frenchman- about 2 hours into the flight he became VERY verbally abusive to the attendant when she - quite reasonably- refused to get him another alcoholic beverage... in his frustration he punched the back of my seat- I did not appreciate that, I stood up and gave him a glare that needed no translation- he stopped, he was obviously too drunk to walk, let alone be a threat, but it didnt stop him from being obnoxious. He cursed out the stewardess every time she walked by.

About 30 minutes later I had the audacity to recline my seat, he threw a fit and hit my chair again- in response I reclined it as much as possible, now both he and I had option of moving to an empty seat elsewhere, but After I had seen him abuse the flight attendants I was NOT interested in making this guys life easier. Around hour 4 I had to go to the bathroom, when I came back I saw that he had straightened my chair to 'the full upright position' and was sitting awkwardly with his knees against the back of my chair so I couldnt recline it- He gave me an arrogant drunken smirk when I returned....like he had won the war... I just smiled at him, went to my seat pressed the recline button and forcefully threw myself into the seat- It reclined all the way - slamming his knees... He screamed and cursed an called the attendant- he spent some time yelling at her about how I had assulted him... She calmed him down, she then came to me and smiled widely and said 'Would you like a complementary drink?'