Man protecting little girl, in a manner of speaking (5)
I believe the answer is:
idiom
'in a manner of speaking' is the definition.
(I've seen this before)
'man protecting little girl' is the wordplay.
'man' becomes 'iom' (Abbreviation for the Isle of Man**).
'protecting' means one lot of letters goes inside another.
'little girl' becomes 'di' (short for Diane, Diana etc).
'iom' enclosing 'di' is 'IDIOM'.
(Other definitions for idiom that I've seen before include "Linguistic peculiarity" , "Characteristic style, vocabulary" , "Group of words in which the meaning may not be obvious" , "Characteristic style of expression" , "Use of words" .)