Social worker is joining those in opposition (5)
I believe the answer is:
antis
'opposition' is the definition.
(I've seen this in another clue)
'social worker is joining' is the wordplay.
'social worker' becomes 'ant' (ants are social insects).
'joining' says to put letters next to each other.
'ant'+'is'='ANTIS'
'those in' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for antis that I've seen before include "People who are opposed" , "the group voting no" , "They say no" , "They oppose" , "They're opposed to" .)