Huge Scotsman in sports car (5)
I believe the answer is:
giant
'huge' is the definition.
(I've seen this before)
'scotsman in sports car' is the wordplay.
'scotsman' becomes 'ian' (common Scottish name).
'in' indicates putting letters inside.
'sports car' becomes 'GT' (abbreviation for grand tourer).
'ian' going inside 'gt' is 'GIANT'.
(Other definitions for giant that I've seen before include "Designating big" , "Extremely large (person)" , "A mighty man like Goliath or Carnera" , "Titan" , "Extremely tall person" .)