They resist difficult puzzles after work (8)
I believe the answer is:
opposers
'they resist' is the definition.
(people who oppose or resist things)
'difficult puzzles after work' is the wordplay.
'difficult puzzles' becomes 'posers' (poser can mean a difficult puzzle or problem).
'after' means one lot of letters go next to another.
'work' becomes 'op' (abbreviation for opus).
'posers' put after 'op' is 'OPPOSERS'.
(Other definitions for opposers that I've seen before include "dissenters" , "adversaries" .)