Oscar classifies fruit (7)
I believe the answer is:
oranges
'fruit' is the definition.
(I've seen this before)
'oscar classifies' is the wordplay.
'oscar' becomes 'o' (phonetic alphabet: alpha, bravo, charlie etc.).
'classifies' becomes 'ranges' (I've seen this before).
'o'+'ranges'='ORANGES'
(Other definitions for oranges that I've seen before include "See 8" , "'Mandarins, say (7)'" , "They are not the only fruit, wrote Jeanette Winterson" , "Navel, blood and Seville are all varieties of these" , "Gear son up for fruit" .)