Case of a trendy position (8)
I believe the answer is:
instance
'case' is the definition.
('instance' can be a synonym of 'case')
'a trendy position' is the wordplay.
'a trendy' becomes 'in'.
'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 "An insect (anag.)" , "Particular case; cite" , "Exemplify" , "A case or example of something" , "Case in point" .)