Collapse as female totally exhausted (4,2)
I believe the answer is:
fall in
'collapse' is the definition.
('fall in' can be a synonym of 'collapse')
'female totally exhausted' is the wordplay.
'female' becomes 'f' (abbreviation).
'totally exhausted' becomes 'allin' (I've seen this before).
'f'+'allin'='FALL-IN'
'as' acts as a link.
(Other definitions for fall in that I've seen before include "Order to troops to take place in formation" , "Army order to take place in formation" , "Military order - take place in formation" , "get dressed?" , "Military order to join formation" .)