Leisure pursuit for the most part involving no associate (6)
I believe the answer is:
hobnob
'associate' is the definition.
(to hobnob with people is to associate with them)
'leisure pursuit for the most part involving no' is the wordplay.
'leisure pursuit' becomes 'hobby' (activity or pursuit done for fun).
'for the most part' means to remove the last letter.
'involving' is an insertion indicator.
'hobby' with its last letter taken off is 'hobb'.
'hobb' going around 'no' is 'HOBNOB'.
(Other definitions for hobnob that I've seen before include "random" , "Socialise as with the rich and famous" , "familiar talk" , "Associate familiarly" , "Talk informally" .)