Scottish hero in defence, brilliant (7)
I believe the answer is:
wallace
'scottish hero' is the definition.
(William Wallace)
'defence brilliant' is the wordplay.
'defence' becomes 'wall' (wall is a kind of defence).
'brilliant' becomes 'ace' (I've seen this before).
'wall'+'ace'='WALLACE'
'in' acts as a link.
(Other definitions for wallace that I've seen before include "Edgar ---, crime writer; an art Collection" , "Edgar -, English thriller writer" , ".Robbie Burns poem 'Scots, wha hae wi' ...... bled'" , "Scottish insurgent" , "With twenty one across, Oscar-winning cartoon pair" .)