What big, mean delinquent has time for diminutive fighter? (12)
I believe the answer is:
bantamweight
'diminutive fighter?' is the definition.
(a relatively light boxer)
'what big mean delinquent has time' is the wordplay.
'delinquent' indicates an anagram (a suspicious or criminal version of the letters).
'has' means one lot of letters goes inside another.
'time' becomes 't' (abbreviation).
'what'+'big'+'mean'='whatbigmean'
'whatbigmean' with letters rearranged gives 'banamweight'.
'banamweight' placed around 't' is 'BANTAMWEIGHT'.
'for' is the link.
(Other definitions for bantamweight that I've seen before include "Boxing category" , "fighter" .)