Rude old bishop on site (7)
I believe the answer is:
obscene
'rude' is the definition.
(obscene can mean rude or indecent)
'old bishop on site' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'bishop' becomes 'B' (chess abbreviation).
'on' means one lot of letters go next to another.
'site' becomes 'scene' (both can mean the location for something).
'o'+'b'+'scene'='OBSCENE'
(Other definitions for obscene that I've seen before include "X-rated" , "unsuitable for children?" , "Repugnant; indecent" , "Rude" , "Lewd or loathsome" .)