Case of trendy position (8)
I believe the answer is:
instance
'case' is the definition.
(I know that case can be written as instance)
'trendy position' is the wordplay.
'trendy' becomes 'in' ('in' can mean fashionable).
'position' becomes 'stance' (stance is a kind of position).
'in'+'stance'='INSTANCE'
'of' acts as a link.
(Other definitions for instance that I've seen before include "Occasion" , "Case in point" , "Particular case; cite" , "'Example, illustration (8)'" , "Particular example" .)