Drinks on small ship, one that pitches (8)
I believe the answer is:
salesman
'one that pitches' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'drinks on small ship' is the wordplay.
'drinks' becomes 'ales' (ale is a kind of drink).
'on' means one lot of letters go next to another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'ship' becomes 'man' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'ales' put after 's' is 'sales'.
'sales'+'man'='SALESMAN'
Can you help me to learn more?
(Other definitions for salesman that I've seen before include "He sells lean mass, strangley" , "''Death of a ...'' (drama by Arthur Miller)" , "He used to be known as a commercial traveller" , "He's a vendor" , "Fermented honey drink" .)