In case of opposite, women are obliged to pay (3)
I believe the answer is:
owe
'are obliged to pay' is the definition.
('they owe' means 'they are obliged to pay')
'in case of opposite women' is the wordplay.
'in' is an insertion indicator.
'case of' says to hollow out the word (remove centre letters) (outsides of).
'women' becomes 'w'.
'opposite' with its centre taken out is 'oe'.
'oe' going around 'w' is 'OWE'.
(Other definitions for owe that I've seen before include "Be beholden" , "Are debtors" , "have favours to return" , "Be in the red" , "Need to pay" .)