Mostly clean quarterdeck for hobby? (7)
I believe the answer is:
pursuit
'for hobby?' is the definition.
(I've seen this before)
'mostly clean quarterdeck' is the wordplay.
'mostly' means to remove the last letter.
'clean' becomes 'pure' (similar in meaning).
'quarterdeck' becomes 'suit' (a suit is one quarter of a deck of cards).
'pure' with its final letter taken off is 'pur'.
'pur'+'suit'='PURSUIT'
(Other definitions for pursuit that I've seen before include "Search" , "courting?" , "The chase or the occupation" , "Occupation; cycle race" , "See 1" .)