By definition trolling is done by a troll, which is:
In Internet slang, a troll is a person who starts quarrels or upsets people on the Internet to distract and sow discord by posting inflammatory and digressive, extraneous, or off-topic messages in an ... Wikipedia
And in some categories, like Politics & Government or Religion, trolling happens continually throughout the day on YA. I'd guesstimate that more than half the questions in P&G or Religion are posted to start a quarrel or upset people. They are typically posted by malcontents who have personal axes to grind.
Other categories, not so much. For example, the Physics category, under Science & Math, rarely has trolling. The questions are typically HS students looking for physics homework help or adults who are interested in science but have little education in it.