American pro dropping ball is a big shock (4)
I believe the answer is:
afro
'shock' is the definition.
(shock can mean a mass of hair)
'american pro dropping ball is a big' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'pro' becomes 'for' (I've seen this in another clue).
'dropping' suggests deleting specific letters.
'ball' becomes 'o' (letter resembling a ball).
'is a big' becomes 'o' (I can't explain this - if you can you should believe this answer much more).
'for' with 'o' removed is 'fr'.
'a'+'fr'+'o'='AFRO'
Can you help me to learn more?
(Other definitions for afro that I've seen before include "Hairdo of the 1960s and 70s" , "Hair in tight curls" , "Shock description" , "configuration of locks" , "Luxuriant (black) hairstyle" .)