Resistance rising in markets supporting out of season dairy product (7,5)
I believe the answer is:
fromage frais
'dairy product' is the definition.
'resistance rising in markets supporting out of season' is the wordplay.
I cannot really see how this works, but
'resistance' could be 'r' (abbreviation) and 'r' is located in the answer.
'of' could be 'o' and 'o' is found within the answer.
'season' could be 'age' and 'age' is present in the answer.
This explanation may well be incorrect...
(Other definitions for fromage frais that I've seen before include "food" , "Low-fat cheese" , "Giraffes roam (anag) - dairy product" , "Soft fresh cheese, like thick yogurt" .)