One aiming to sell diamond surrounds this sportsman (7)
I believe the answer is:
pitcher
'diamond surrounds this sportsman' is the definition.
'pitcher' can be an answer for 'sportsman' (I have seen 'American sportsman' mean 'pitcher' so perhaps 'sportsman' could also mean 'pitcher'). I am unsure of the rest of the definition.
'one aiming to sell' is the wordplay.
'one aiming' becomes 'er' (I can't explain this - if you can you should give a lot more credence to this answer).
'to' means one lot of letters go next to another (I've seen this in other clues).
'sell' becomes 'pitch' (pitching is a kind of selling).
'er' put after 'pitch' is 'PITCHER'.
Can you help me to learn more?
(Other definitions for pitcher that I've seen before include "that can hold his drink" , "Does one throw the vessel?" , "Baseball bowler and vessel for liquid" , "crock" , "Baseball player; big jug" .)