One wasn't there to make such a defence (5)
I believe the answer is:
alibi
'such a defence' is the definition.
(defence given to police by a suspect)
'one wasn't there' is the wordplay.
I cannot really understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
The remaining letters 'albi' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'to make' acts as a link.
Can you help me to learn more?
(Other definitions for alibi that I've seen before include "Legal defence proving innocence" , "Evidence one was not at crime scene" , "Excuse, defence" , "Excuse for not doing something" , "Fact of being elsewhere (legal)" .)