Piggy beginning to crawl in, occupying hole (7)
I believe the answer is:
porcine
'piggy' is the definition.
('porcine' can be a synonym of 'piggy')
'beginning to crawl in occupying hole' is the wordplay.
'beginning to' indicates taking the first letters.
'occupying' is an insertion indicator.
'hole' becomes 'pore' (pore is a kind of hole**).
The initial letter of 'crawl' is 'c'.
'c'+'in'='cin'
'cin' going into 'pore' is 'PORCINE'.
(Other definitions for porcine that I've seen before include "Resembling a pig" , "Filthy" , "Piggish" , "Corn pie (anag.)" , "Swinish" .)