Such situations almost always happen unintentionally. All it has to do is for the authority figure to believe that his subordinate is violent, to make them more violent. As said above, this is like a placebo effect, where the "experimenter" is the authority figure and the "subjects" are his subordinates. Because the authority figure believes that he is violent prior to the event, he will interpret his subordinates' actions to be more violent than it actually is.
Such situations are common in situations such as police brutality, controlling parenting, and other hierarchical relationships. The "abuser" almost always don't realize that they are doing something evil. They feel that their behavior is legitimate, given that they think that their subordinates are perceived to be evil.
That's another reason why you take the words of any Wikipedia administrator, forum moderator, or teacher, with only a grain of salt. If they accuse another of "trolling" or "bullying", it's often a mere perceived evil. None of their words may be an accurate representation of the supposed "bully".
Often "bullies" are "evil" only because others falsely accuse them of an alleged wrong. But, ironically, the accusers themselves are also often wrong.
People rationalize. And they also rationalize their friends' behavior. For example, suppose a teacher saw some other teacher yelling and apparently abusing a student. But he won't accuse him as malicious, partially because he thinks adults aren't as mean as children, and partially because he is his friend so he would rationalize his behavior as non-malicious.
Why are people who are abused by authority figures "assumed" bad? Such as the incident in which the police tased a student and the student responded "don't taze me bro."
People hypnotize each other. For example, when they are accused of something, they will apparently believe that the accusation is true.
For example, the victim of the "don't taze me bro" incident actually believed that he did something "wrong", even though at the time of the incident, he didn't believe he did anything wrong.
A "bully" can be a person who stands up for himself, a person who disobeys authority, or a rebel who wants to do things his own way.
I don't believe that "bullies" or "trolls" exist as commonly perceived. Then why do some many people believe that they do exist? It's partially caused from the placebo effect as described above, and then exaggerated through the media. Television shows commonly show that people who often do evil things actually have an evil personality. This is far from reality. It's even undetermined if the "bully's" actions were malicious or negligent, or whether if it's a whole misunderstanding.
I may write a series of posts explaining why so many accused "bullies" weren't bullying at all.