Collapse as fellow has trouble (4)
I believe the answer is:
fail
'collapse' is the definition.
(I've seen this before)
'fellow has trouble' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'has' means one lot of letters go next to another.
'trouble' becomes 'ail' (synonyms).
'f'+'ail'='FAIL'
'as' is the link.
(Other definitions for fail that I've seen before include "Flunk" , "Be unsuccessful, say in exam" , "Let down" , "Stop working properly" , "Break down" .)