First hint of scrapper's face becoming puffed up (4)
I believe the answer is:
smug
'puffed up' is the definition.
(I've seen this in another clue)
'first hint of scrapper's face' is the wordplay.
'first' means one lot of letters go next to another.
'hint of' says to take the initial letters (the smallest possible amount of the word).
'face' becomes 'mug' (informal term for face).
The initial letter of 'scrappers' is 's'.
's' put next to 'mug' is 'SMUG'.
'becoming' acts as a link.
(Other definitions for smug that I've seen before include "Steal" , "Smooth" , "Irritatingly self-satisfied" , "Unctuous" , "Full of oneself" .)