Bit of a grimace from a Scot (3)
I believe the answer is:
mac
'a scot' is the definition.
(many Scottish surnames begin with Mac)
'bit of a grimace from' is the wordplay.
'bit of' indicates the answer is hidden within the clue.
'MAC' is hidden within 'grimace from'.
(Other definitions for mac that I've seen before include "Waterproof coat (colloq.)" , "laptop?" , "A rainproof" , "one used in shower?" , "It may help you keep dry" .)