http://www.theguardian.com/world/feedarticle/11506312
According to the story...
UA1462 Newark to Denver flight diverted to Chicago after heated argument. The lady in front threw water over the gentleman behind, who had used a Knee Defender and disregarded FA instruction to remove it.
Also says neither passenger arrested, which if the other details are accurate, I really hope is not the case.
Using the Knee Defender is completely illegal.
When I buy a ticket for a specific class of service and that class includes a seat that reclines it is might right to recline it. If you cannot accept the fact that the person in front of you wants to be comfortable, buy a ticket in a different class of service where you don't have to worry about it.