Misfortune of model featuring in commercial so (9)
I believe the answer is:
adversity
'misfortune' is the definition.
(adversity is a kind of misfortune)
'model featuring in commercial so' is the wordplay.
'model' becomes 'sit' (e.g. for a painting).
'featuring in' indicates putting letters inside.
'commercial' becomes 'ad' (abbreviation for advertisement).
'so' becomes 'very' (I've seen this before).
'ad'+'very'='advery'
'sit' inserted into 'advery' is 'ADVERSITY'.
'of' is the link.
(Other definitions for adversity that I've seen before include "Hard times or misfortune" , "Misfortune, hardship" , "State of misfortune or affliction" , "Circumstances that cause trouble or sorrow" .)