Old coin Scottish architect used to secure team backing (8)
I believe the answer is:
sixpence
'old coin' is the definition.
(I've seen this before)
'scottish architect used to secure team backing' is the wordplay.
'scottish architect' becomes 'Spence' (Basil Spence, 1907-1976).
'used to secure' indicates putting letters inside.
'team' becomes 'XI' (a football team, from Roman numerals for 11).
'backing' is a reversal indicator.
'xi' reversed gives 'ix'.
'spence' placed around 'ix' is 'SIXPENCE'.
(Other definitions for sixpence that I've seen before include "'Tanner' (coin)" , "Old coin worth two and a half new pence" , "6d" , "Pre-decimal coin" , "bit dated" .)