Victor Hugo's beginning to get into party (5)
I believe the answer is:
champ
'victor' is the definition.
(I've seen this in another clue)
'hugo's beginning to get into party' is the wordplay.
'beginning to' suggests taking the first letters.
'get into' indicates putting letters inside.
'party' becomes 'camp' (both can mean a group of people).
The first letter of 'hugos' is 'h'.
'h' inserted inside 'camp' is 'CHAMP'.
(Other definitions for champ that I've seen before include "Title holder (abbr)" , "Gnaw; winner (abbr.)" , "Munch noisily; winner" , "Chew noisily" , "Victor (slang)" .)