Flag seen when queen is captured by bishop and rook (6)
I believe the answer is:
banner
'flag' is the definition.
(banner is a kind of flag)
'queen is captured by bishop and rook' is the wordplay.
'queen' becomes 'anne' (Queen Anne, 18th-century queen).
'is captured by' indicates putting letters inside.
'bishop' becomes 'B' (abbreviation for bishop in chess).
'and' means one lot of letters go next to another.
'rook' becomes 'R' (chess abbreviation).
'b'+'r'='br'
'anne' inserted into 'br' is 'BANNER'.
'seen when' is the link.
(Other definitions for banner that I've seen before include "Flag with a slogan" , "The flag for one who prohibits" , "Knight's standard" , "protester's statement?" , "Tree product; series of games" .)