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' means one lot of letters goes inside another.
'bishop' becomes 'B' (abbreviation for bishop in chess).
'and' says to put letters next to each other.
'rook' becomes 'R' (chess abbreviation).
'b'+'r'='br'
'anne' put 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" .)