When caught only cuddling (4)
I believe the answer is:
once
'when' is the definition.
(synonyms)
'caught only cuddling' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'only' becomes 'one' (synonyms).
'cuddling' is an insertion indicator (inserted letters are embraced or welcomed in).
'c' going inside 'one' is 'ONCE'.
(Other definitions for once that I've seen before include "In former times" , "A single time" , "Formerly, at one time" , "At a previous time" , "On a single (or past) occasion" .)