Romeo stands in ruin — an occupier of position by entrance (7)
I believe the answer is:
doorman
'occupier of position by entrance' is the definition.
(someone who stands by an entrance)
'romeo stands in ruin an' is the wordplay.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'stands in' is an insertion indicator.
'ruin' becomes 'doom' (doom means ruin or disaster).
'r' placed within 'doom' is 'doorm'.
'doorm'+'an'='DOORMAN'
(Other definitions for doorman that I've seen before include "Gatekeeper" , "Entrance attendant" , "Hall porter" , "Janitor" , "Bouncer" .)