Harass the bosses in difficulty (6)
I believe the answer is:
obsess
'harass' is the definition.
(thesaurus)
'bosses in difficulty' is the wordplay.
'in difficulty' indicates an anagram (I've seen this in other clues).
'bosses' with letters rearranged gives 'OBSESS'.
'the' is the link.
(Other definitions for obsess that I've seen before include "Bosses (anag.)" , "Constantly worry (about something)" , "Prey on" , "Be constantly preoccupied" , "Be constantly talking about" .)