Offensive posters prompted by promenade cycling (6)
I believe the answer is:
trolls
'offensive posters' is the definition.
(people who post online in an offensive way)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for trolls that I've seen before include "They start rows on the internet" , "Ugly cave-dwelling creatures" , "Scandinavian goblins" , "Mythical Scandinavian dwarfs" , "Mythical Scandinavian cave dwellers" .)