On the off chance both sides do it without repeating it (4)
I believe the answer is:
once
'without repeating it' is the definition.
I can't judge whether this defines the answer.
'on the off chance both sides do it' is the wordplay.
'the off chance both sides do' becomes 'c' (I am not sure about this - if you are sure you should believe this answer much more).
'it' becomes 'e' ('e' can mean 'electronic' which is similar to 'IT').
'on'+'c'+'e'='ONCE'
Can you help me to learn more?
(Other definitions for once that I've seen before include "yesterday" , "In times past" , "Quick examination" , "Formerly; as soon as" , "in bygone days" .)