Following people inside with joint leader (8)
I believe the answer is:
flagship
'leader' is the definition.
(I have seen 'leader of fleet' mean 'flagship' so perhaps 'leader' could also mean 'flagship')
'following people inside with joint' is the wordplay.
'following' becomes 'f.' (used when citing page numbers etc).
'people inside' becomes 'lags' (lag can informally mean a convict).
'with' says to put letters next to each other.
'joint' becomes 'hip' (part of body).
'f'+'lags'+'hip'='FLAGSHIP'
(Other definitions for flagship that I've seen before include "An organisation's most important thing" , "Pre-eminent item" , "Most important part of a group" , "It carries the commander of the fleet" , "leader of fleet" .)