Bar occupied by old William Archer (6)
I believe the answer is:
bowman
'archer' is the definition.
(synonyms)
'bar occupied by old william' is the wordplay.
'bar' becomes 'ban' (both can mean to outlaw or block).
'occupied by' is an insertion indicator.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'william' becomes 'wm'.
'o'+'wm'='owm'
'ban' going around 'owm' is 'BOWMAN'.
(Other definitions for bowman that I've seen before include "Missile launcher" , "violinist!" , "one of The Archers" , "Archer" , "Tell" .)