Right to enter large ship (4)
I believe the answer is:
brig
'ship' is the definition.
(I've seen this before)
'right to enter large' is the wordplay.
'right' becomes 'r' (common abbreviation).
'to enter' is an insertion indicator.
'large' becomes 'big' ('big' can be a synonym of 'large'**).
'r' inserted within 'big' is 'BRIG'.
(Other definitions for brig that I've seen before include "Crew can" , "Two-masted square-rigger" , "Two-masted square rigger" , "Two-masted square-rigged sailing ship" , "Two-master; army officer (abbr.)" .)