Realist oddly supports Left in painting (8)
I believe the answer is:
portrait
'painting' is the definition.
(portrait is a kind of painting)
'realist oddly supports left' is the wordplay.
'oddly' indicates alternate letters.
'supports' means one lot of letters go next to another (bottom letters provide a support for the top ones).
'left' becomes 'port' (left side of a ship - opposite of starboard).
The alternating letters of 'realist' are 'rait'.
'rait' put after 'port' is 'PORTRAIT'.
'in' acts as a link.
(Other definitions for portrait that I've seen before include "(Person's) painting" , "characteristic depiction" , "Artistic representation (of a person)" , "Painted likeness of a person" , "Type of painting" .)