Google search produced:

"From the fishing term. As a noun, synonymous with flamebait. As a verb, to post controversial or provocative messages in a deliberate attempt to provoke flames."

I guess that the fishing reference is from Americans who pronounce troll exactly like trawl and hence are unaware that in real English they are, in fact, two distinct words. ;o)

I felt that PeterH's postings became troll-like when I had to explain for the third time that crop-planting was just an incidental aspect of my post and I was not proposing any particular view on the subject that needed to be backed up by the evidence that he kept demanding.